ABSTRACT
Background
Evidence is lacking to determine whether there have been any changes in dietary or total usual intakes of vitamin D among Canadians, in the light of recent evidence of beneficial health effects beyond bone.
Objective
We aimed to examine trends in dietary and total usual intake of vitamin D among Canadians aged ≥1 y.
Methods
This study used nationally representative nutrition data from the Canadian Community Health Survey Cycle 2.2 (CCHS 2004) and CCHS Nutrition in 2015. Dietary intake data were collected with use of two 24-h dietary recalls and dietary supplement use was determined by questionnaire. The National Cancer Institute method was used to estimate the usual intake of vitamin D as well as the prevalence of vitamin D inadequacy among Canadians aged ≥1 y.
Results
From 2004 to 2015, the usual intake of vitamin D from food significantly decreased (P < 0.05) by 1 μg/d only in vitamin D supplement nonusers. The contribution of Milk and Alternatives food group (i.e., fluid milk, fortified soy beverages, powdered milk, and other milk alternatives) to dietary vitamin D intake significantly decreased (P < 0.05) in both supplement users (by 7.1%) and nonusers (by 5.8%). Prevalence of vitamin D supplement use and percentage contribution of vitamin D from supplemental sources significantly increased (P < 0.05) by 5.0% and 14.9%, respectively, from 2004 to 2015. Total usual intake of vitamin D (food + supplement) significantly increased (P < 0.05) from 15.1 ± 0.3 μg/d in 2004 to 31.5 ± 1.8 μg/d in 2015 in vitamin D supplement users. In contrast to vitamin D supplement nonusers, the prevalence of vitamin D inadequacy significantly decreased (P < 0.05) from 20.6% to 14.1% among users of vitamin D supplements.
Conclusions
The prevalence of vitamin D supplement use and the percentage contribution of vitamin D from supplemental sources has increased in the Canadian population over an 11-y period.
Keywords: vitamin D, supplement use, usual intake, Canadians, prevalence of inadequacy
Introduction
Vitamin D is an essential fat-soluble vitamin with well-established effects on calcium and phosphate metabolism, skeletal health, and risk of falls and fractures (1, 2). Vitamin D exists in 2 distinct forms, ergocalciferol (vitamin D2), which is obtained from fungi (mushrooms and yeast) sources, and cholecalciferol (vitamin D3), which is produced in the epidermal layer of skin through UV exposure and obtained from animal sources (3). Based on bone health outcomes, the Institute of Medicine (IOM) provided the current DRIs for vitamin D in 2011, with the RDA ranging from 600 IU/d for children aged 1 y to 800 IU/d for the elderly (4, 5). In Canada, sun exposure capable of inducing cutaneous vitamin D synthesis is available for only 6–7 mo/y, and the UV radiation is highest in the southernmost latitudes (6). In addition, people who have darker skin color because of higher melanin content have trouble synthesizing vitamin D from the sun (7, 8). Thus, as the cutaneous synthesis of vitamin D depends on many factors such as skin pigmentation, latitude, season, outdoor activity, the duration of sun exposure, and the amount of skin exposed, the recommendations for vitamin D were determined specifically by the IOM committee based on the assumption of minimal or no sun exposure (4, 5). Fish liver oils (such as cod liver oil) and flesh of fatty fish (such as salmon) are among the best sources of vitamin D, and small amounts are found in beef liver, egg yolks, and cheese (7). However, as adequate intake of vitamin D is unlikely to be achieved through intakes of unfortified foods (9, 10), this can be addressed by fortification programs and vitamin D supplement use. In Canada, in addition to mandatory fortification of margarine, and cow milk and milk substitutes, voluntary fortification with vitamin D is permitted in some foods such as egg products (mandatory if there is a reduction in the vitamin D content), condensed milk, goat milk, goat milk powder, and butter substitutes (11).
Ensuring adequate intake of vitamin D is essential throughout the lifespan to prevent rickets and skeletal deformities in children and osteomalacia and osteoporosis in adults (1). However, in recent years, a growing body of evidence suggests that vitamin D is not only involved in bone metabolism but can also affect the development of many other disease states including cardiovascular diseases, chronic kidney disease, cancer, metabolic syndrome, autoimmune disorders, and infectious diseases (12–17). Thus, considering the beneficial effects of vitamin D on various diseases, it is essential to assess the vitamin D intake of the Canadian population over time to inform policymakers and decisionmakers (18).
There are no reports available in the literature determining whether there has been a change in dietary or total usual intakes of vitamin D among Canadians, in light of recent evidence of beneficial health effects beyond bone. With use of nutrition data from 2 nationally representative surveys of Canadians, conducted in 2004 and 2015, we examined trends in dietary and total usual vitamin D intake over 11 y. Other objectives were to 1) assess the contribution of Enriched Beverages and Food Groups to usual dietary vitamin D intake; 2) report the prevalence of vitamin D inadequacy among both vitamin D supplement users and nonusers; and 3) determine and compare the factors associated with vitamin D supplement use in 2004 and 2015.
Methods
Study population
This study used nutrition data from the Canadian Community Health Survey Cycle 2.2 (CCHS 2004) and CCHS Nutrition in 2015. The overall response rate was 62% in CCHS 2015 and 76.5% in CCHS 2004 (19, 20). These nationally representative cross-sectional surveys were conducted by Statistics Canada and included Canadians who resided in the 10 provinces. The CCHS 2004 and 2015 data were collected from 35,107 and 20,487 survey respondents, respectively. Dietary intake data were collected from 24-h dietary recalls at 2 time points. The first 24-h dietary recall was administered to the whole sample and the second 24-h dietary recall was administered to about one-third of the sample in both surveys. Dietary data were collected with the automated multiple pass method (computer-assisted personal interview) on the first 24-h recall at home; this method was based on that from the USDA (21). The second 24-h recall was collected by a telephone interview at home. Data on children aged 1–6 y were collected by proxy interviews, whereas children aged 6–12 y were interviewed under parental supervision. A nonproxy method of data collection was applied to individuals aged ≥12 y (19, 20). Permission to access and conduct the analysis of CCHS 2004 and 2015 data was obtained from the Research Data Center Program of Statistics Canada. In addition to dietary data, data related to sociodemographic status, such as age, sex, area of residence, immigration status, BMI, food security status, smoking status, education, and income, were also collected. Details about the sampling approach and questionnaires can be found elsewhere (19, 20).
Analytical sample
The current study is representative of 30,074,236 Canadians in 2004 and 33,946,610 in 2015 who were aged ≥1 y and had provided plausible dietary information. We excluded data from children aged <1 y, pregnant and lactating women, individuals who reported no food intake in the 24-h recall, those with extremely high intakes of nutrients, and individuals who reported <200 kcal or >8000 kcal daily energy intake. The same inclusion and exclusion criteria were applied to both 2004 and 2015 data.
Dietary and supplemental vitamin D
When collecting data via 24-h recall (both 2004 and 2015), the respondents were asked about the type of food, amount of food, food occasion and location, and dietary supplement intake. In CCHS 2015, respondents were asked about any supplement use in the last 24 h. Additional detailed information on supplement intake was also obtained, such as frequency and amount of supplement intake, product information, and natural product number of supplements. In CCHS 2004, unlike 2015, supplement use information was obtained over the past 30 d. Similarly, the detailed information regarding supplement use including frequency, duration of use, complete product information, drug identification number, natural product number, and the mean amount taken per day was obtained in CCHS 2004.
Definitions and covariates
A vitamin D supplement user was defined as any individual who reported taking any supplement that contained vitamin D during the dietary recall. Similarly, a vitamin D supplement nonuser was defined as an individual who did not report taking any supplement containing vitamin D during the dietary recall. For the analysis, categorical variables including DRI age groups (children 1–3 y, children 4–8 y, males 9–13 y, females 9–13 y, males 14–18 y, females 14–18 y, males 19–30 y, females 19–30 y, males 31–50 y, females 31–50 y, males 51–70 y, females 51–70 y, males ≥71 y, females ≥71 y), food secure (yes, no), university degree (yes, no), area of residence (urban, rural), household income (decile 1–5, decile 6–10), and pre-existing chronic conditions (if an individual had been diagnosed with any of the following diseases: diabetes, heart disease, cancer, osteoporosis, and hypertension) (yes, no) were used unless otherwise specified. We also analyzed the vitamin D intake from Enriched Beverages and different Food Groups: “Vegetables and Fruit,” “Grain Products” (whole grain and non-whole grain), “Milk and Alternatives” (fluid milk, fortified soy beverages, powdered milk and other milk alternatives such as cheese, yogurt), “Meat and Alternatives” [beef, game and organ meat, other meats (pork, veal, lamb), poultry, fish, shellfish, legumes, nuts and seeds, eggs, processed meats] and “Other Food and Beverages.”
Vitamin D requirements
The IOM set the estimated average requirement (EAR) of vitamin D at 10 μg/d for all ages >1 y and the tolerable upper intake level (UL) of vitamin D at 63 μg/d for children aged 1–3 y, 75 μg/d for children 4–8 y, and 100 μg/d for other DRI age groups (5). We used EAR cutoffs to determine the prevalence of inadequacy of vitamin D intake.
Statistical methods
Separate analyses were conducted for both 2004 and 2015 survey data. Values are represented in percentages (± SE) and means (± SE) where required. The results obtained in 2004 and 2015 were tested for significance based on nonoverlapping 95% CI (P < 0.05) (22). Descriptive analysis was carried out to explore the percentage of the population reporting use of vitamin D supplements. With use of Canada's Food Guide 2007, we determined the percentage contribution of 4 Food Groups (i.e., Vegetables and Fruit, Grain Products, Milk and Alternatives, and Meat and Alternatives) as well as other foods and beverages to usual dietary vitamin D intake (23). To determine the association between vitamin D supplement use and sociodemographic variables such as sex, education, food security status, area of residence, income deciles, a chronic conditions chi-square test was used. With use of a multiple logistic regression model, associations between vitamin D supplement use and age, sex, income, education, food security, chronic conditions, and area of residence were evaluated. Weighting and bootstrapping weights were applied to produce population-level estimates as per the recommendations by Statistics Canada (24); α was set at 0.05. SAS software (SAS Institute), version 9.4, was used to perform all the analyses in the study.
We used National Cancer Institute (NCI) methods (25) to determine the usual intake of vitamin D. NCI methods were also used to determine the prevalence of inadequacy for vitamin D (% below the EAR). NCI analysis requires at least 2 sets of 24-h recall data; therefore, data from both days of recall were used. In this NCI analysis, the following covariates were used: 1) sequence of the 24-h recall, categorized as day 1 or day 2; 2) the day of the week when the 24-h recall data was reported, categorized as weekdays and weekends; 3) energy consumption from food during the 24-h recall; and 4) age/sex groups. For NCI analyses, of the 2 potential models, the amount model or probability model, we chose the amount model as vitamin D is usually taken every single day (23). We used the MIXTRAN and DISTRIB macros developed by NCI (26) to estimate the usual intakes of vitamin D, with a slight modification to account for use of appropriate bootstrapping weights. Further details about the NCI method and the SAS macros can be found at the NCI website (25).
Results
Trends in dietary and total usual vitamin D intake
Trends in dietary and total usual vitamin D intake and the prevalence of inadequacy among vitamin D supplement users and nonusers are reported in Table 1 (2004 and 2015), by age-specific and sex-specific groups. Among vitamin D supplement nonusers, the usual intake of vitamin D from food sources significantly decreased (P < 0.05) from 2004 to 2015 in most age groups and sex groups, especially for those aged <51 y. Dietary vitamin D intake of supplement nonusers significantly decreased (P < 0.05) from 5.2 ± 0.1 μg/d in 2004 to 4.2 ± 0.2 μg/d in 2015 across all individuals (all age/sex groups combined).
TABLE 1.
Intake of vitamin D and prevalence of vitamin D inadequacy among Canadian supplement users and nonusers in 2004 and 2015 among Canadians across age and sex groups1
| Nonusers—2004 (n = 21,622,372) | Nonusers—2015 (n = 22,714,586) | Users—2004 (n = 8,451,866) | Users—2015 (n = 11,232,024) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Age and sex groups | Vitamin D from food, μg/d2 | % below EAR3 | Vitamin D from food, μg/d2 | % below EAR3 | Vitamin D from food, μg/d2 | Vitamin D from food and supplement, μg/d2 | % below EAR3 | Vitamin D from food, μg/d2 | Vitamin D from food and supplement, μg/d2 | % below EAR3 |
| All children | ||||||||||
| 1–8 y4 | 4.7 ± 0.1 | 95.7 ± 0.7 | 4.1 ± 0.2 | 99.0 ± 0.4† | 4.9 ± 0.2 | 13.4 ± 0.2 | 19.0 ± 1.3 | 5.3 ± 0.3 | 16.7 ± 1.1* | 38.0 ± 3.4† |
| Females | ||||||||||
| 9–13 y | 5.2 ± 0.1 | 93.5 ± 1.0 | 4.5 ± 0.2 | 97.6 ± 0.8† | 5.7 ± 0.3 | 13.5 ± 0.4 | 25.8 ± 3.3 | 5.5 ± 0.3 | 20.8 ± 1.4* | 27.8 ± 3.3 |
| 14–18 y | 5.1 ± 0.1 | 93.5 ± 1.0 | 4.2 ± 0.2* | 97.3 ± 0.9† | 5.5 ± 0.3 | 13.1 ± 0.4 | 29.0 ± 3.4 | 5.5 ± 0.3 | 24.0 ± 1.5* | 21.9 ± 2.6 |
| 19–30 y | 4.7 ± 0.1 | 94.9 ± 0.9 | 3.8 ± 0.2* | 98.3 ± 0.6† | 4.9 ± 0.2 | 13.1 ± 0.4 | 27.1 ± 2.8 | 5.2 ± 0.4 | 27.7 ± 1.7* | 14.2 ± 1.7† |
| 31–50 y | 4.5 ± 0.1 | 95.6 ± 0.9 | 3.6 ± 0.2* | 98.6 ± 0.6 | 4.6 ± 0.2 | 14.9 ± 1.1 | 24.7 ± 2.5 | 4.8 ± 0.3 | 31.3 ± 1.9* | 12.0 ± 1.8† |
| 51–70 y | 4.0 ± 0.1 | 97.2 ± 0.6 | 3.3 ± 0.1 | 98.6 ± 0.5 | 4.3 ± 0.2 | 16.3 ± 0.5 | 20.0 ± 1.7 | 4.4 ± 0.3 | 36.2 ± 2.1* | 8.2 ± 1.4† |
| ≥71 y | 3.6 ± 0.1 | 98.2 ± 0.5 | 2.9 ± 0.2 | 99.2 ± 0.4 | 3.8 ± 0.2 | 15.9 ± 0.5 | 19.8 ± 2.1 | 4.0 ± 0.2 | 41.2 ± 2.5* | 5.4 ± 1.2† |
| Males | ||||||||||
| 9–13 y | 6.3 ± 0.2 | 86.6 ± 1.5 | 5.0 ± 0.2* | 94.6 ± 1.3† | 6.6 ± 0.3 | 14.7 ± 0.4 | 18.6 ± 2.6 | 6.3 ± 0.4 | 19.2 ± 1.3* | 31.6 ± 3.1† |
| 14–18 y | 7.2 ± 0.2 | 80.1 ± 1.8 | 5.5 ± 0.2* | 90.6 ± 1.6† | 7.8 ± 0.5 | 16.7 ± 0.6 | 16.7 ± 2.7 | 7.6 ± 0.5 | 24.5 ± 1.7* | 21.2 ± 2.8 |
| 19–30 y | 6.7 ± 0.2 | 83.6 ± 1.8 | 5.3 ± 0.2* | 92.5 ± 1.6† | 7.5 ± 0.6 | 15.4 ± 0.6 | 19.3 ± 3.7 | 7.7 ± 0.7 | 28.3 ± 2.0* | 13.0 ± 2.4 |
| 31–50 y | 6.0 ± 0.2 | 87.0 ± 1.5 | 4.8 ± 0.2* | 93.8 ± 1.3† | 6.4 ± 0.4 | 15.2 ± 0.5 | 17.5 ± 2.8 | 5.9 ± 0.4 | 31.1 ± 1.9* | 13.4 ± 2.1 |
| 51–70 y | 5.0 ± 0.2 | 93.2 ± 1.1 | 4.2 ± 0.2 | 95.7 ± 1.1 | 5.7 ± 0.3 | 15.8 ± 0.6 | 16.6 ± 2.5 | 5.6 ± 0.4 | 35.6 ± 2.1* | 8.3 ± 1.6† |
| ≥71 y | 4.2 ± 0.1 | 96.2 ± 0.8 | 3.6 ± 0.2 | 98.0 ± 0.7 | 4.8 ± 0.3 | 17.0 ± 0.8 | 14.1 ± 2.7 | 4.7 ± 0.3 | 39.9 ± 2.4* | 6.2 ± 1.2† |
| All participants | 5.2 ± 0.1 | 91.9 ± 1.0 | 4.2 ± 0.2* | 96.5 ± 0.8† | 5.2 ± 0.2 | 15.1 ± 0.3 | 20.6 ± 1.1 | 5.1 ± 0.3 | 31.5 ± 1.8* | 14.1 ± 1.8† |
Analysis was conducted separately for 2004 and 2015 data sets (18, 19). EAR, estimated average requirement.
Values are presented as mean ± SE.
Values are presented as mean of percentages ± SE.
Data reported are for collapsed age groups of children 1–3 y and children 4–8 y.
Significant differences (P < 0.05) between vitamin D intakes from 2004 to 2015 were tested by CI overlapping technique (22).
Total usual intake of vitamin D (food + supplement) significantly increased (P < 0.05) in all age-specific and sex-specific groups from 2004 to 2015 (Table 1). It significantly increased (P < 0.05) from 15.1 ± 0.3 μg/d in 2004 to 31.5 ± 1.8 μg/d in 2015 across all individuals (all age/sex groups combined).
Prevalence of vitamin D inadequacy in 2004 and 2015
Table 1 lists the results of NCI analysis, which includes the usual intake and prevalence of inadequacies of vitamin D. The prevalence of vitamin D inadequacy significantly increased (P < 0.05) from 91.9% in 2004 to 96.5% in 2015 in vitamin supplement nonusers (Table 1). The prevalence of inadequacy significantly decreased (P < 0.05) from 20.6% in 2004 to 14.1% in 2015. Although most age/sex groups of users showed improvement inadequacy, some did not (Table 1). For example, the prevalence of inadequacy rose in children aged 1–8 y despite an increase in food and supplement intake. Furthermore, among all participants, the % above the UL was <3% with very low frequencies across subgroups based on supplement use and age/sex. The % above UL was around 3% only for women aged ≥71 y.
Food sources of vitamin D in 2004 and 2015
Table 2 provides information on the percentage contribution of Food Groups from Canada's Food Guide (2007) and Enriched Beverages to dietary vitamin D intake in 2004 and 2015. From 2004 to 2015, the proportion of vitamin D obtained from “Meat and Alternatives,” “Milk and Alternatives,” and “Vegetables and Fruit” among vitamin D supplement nonusers significantly decreased (P < 0.05) by 8.0%, 5.8%, and 0.4%, respectively. Conversely, the percentage contribution of “Grain Products” and Enriched Beverages to dietary vitamin D intake significantly increased (P < 0.05) from 0.06% to 5.7% and from 0.86% to 2.1%, respectively. Among vitamin D supplement users, vitamin D intake from “Vegetables and Fruit,” “Milk and Alternatives,” and “Meat and Alternatives” was significantly decreased in 2015 compared to 2004. Although, there was a significant increase (P < 0.05) in vitamin D intake from “Grain Products,” “Other Foods and Beverages,” and Enriched Beverages.
TABLE 2.
Contribution (%) of Enriched Beverages and 5 Food Groups of Canada's Food Guide to dietary vitamin D intake in vitamin D supplement users and nonusers in 2004 and 2015 among Canadians across age and sex groups1
| 2004 | 2015 | |||
|---|---|---|---|---|
| Supplement nonusers (n = 21,622,372) | Supplement users (n = 8,451,866) | Supplement nonusers (n = 22,714,586) | Supplement users (n = 11,232,024) | |
| Food Groups and Enriched Beverages | ||||
| Vegetables and Fruit, % | 1.4 ± 0.1 | 1.6 ± 0.2 | 1.0 ± 0.1* | 1.1 ± 0.1† |
| Grain Products, % | 0.06 ± 0.01 | 0.06 ± 0.01 | 5.7 ± 0.2* | 5.0 ± 0.3† |
| Milk and Alternatives, % | 41.3 ± 0.4 | 42.4 ± 0.6 | 35.5 ± 0.6* | 35.3 ± 0.8† |
| Meat and Alternatives, % | 25.8 ± 0.3 | 25.5 ± 0.6 | 17.8 ± 0.5* | 17.5 ± 0.6† |
| Other Foods and Beverages, % | 15.9 ± 0.03 | 15.2 ± 0.4 | 15.7 ± 0.4 | 16.4 ± 0.6† |
| Enriched Beverages, % | 0.86 ± 0.01 | 1.7 ± 0.2 | 2.1 ± 0.2* | 3.6 ± 0.3† |
| Vitamin D fortified foods (mandatory and voluntary) | ||||
| Fluid milk, soy beverages, and powdered milk,2 % | 36.3 ± 0.4 | 37.9 ± 0.6 | 27.1 ± 0.5* | 27.8 ± 0.8† |
| Margarine, % | 15.8 ± 0.3 | 5.5 ± 0.2 | 17.3 ± 0.4* | 6.9 ± 0.3† |
Values are represented as mean of percentages ± SE and analysis was conducted separately for 2004 and 2015 data sets (18, 19). CCHS, Canadian Community Health Survey.
Powdered milk is under the mandatory fortification regulations of Canada (11).
Significant difference (P < 0.05) between CCHS 2004 and 2015 among supplement nonusers by CI overlapping technique (22).
Significant difference (P < 0.05) between CCHS 2004 and 2015 among supplement users by CI overlapping technique (22).
In 2015, as reported in Table 2, vitamin D fortified milk accounted for 27.1% and 27.8% of total vitamin D intake from food sources in vitamin D supplement nonusers and users, respectively. Vitamin D fortified margarine also accounted for 17.3% and 6.9% of total vitamin D intake from food sources in vitamin D supplement nonusers and users, respectively.
Percentage of vitamin D obtained from supplemental sources in 2004 and 2015
As shown in Table 3, from 2004 to 2015, the percentages of vitamin D obtained from supplemental sources significantly increased (P < 0.05) in all age-specific and sex-specific groups, except children aged 1–8 y and females aged 9–13 y. Overall, the percentage contribution of supplemental sources of vitamin D to daily intake significantly increased (P < 0.05) from 63.2% in 2004 to 78.1% in 2015 among Canadian vitamin D supplement users.
TABLE 3.
Percentages of vitamin D obtained from supplemental sources among vitamin D supplement users across age and sex groups of Canadians in 2004 and 20151
| 2004 | 2015 | |||
|---|---|---|---|---|
| (n = 8,451,866) | (n = 11,232,024) | |||
| Age/sex groups | n | % | n | % |
| Children2 | ||||
| 1–3 y | 1,063,185 | 57.6 ± 1.1 | 1,179,813 | 61.8 ± 2.5 |
| 4–8 y | 60.4 ± 0.9 | 61.6 ± 2.0 | ||
| Females | ||||
| 9–13 y | 228,140 | 56.5 ± 1.6 | 250,956 | 61.9 ± 3.0 |
| 14–18 y | 166,302 | 60.3 ± 1.9 | 193,856 | 70.0 ± 3.0* |
| 19–30 y | 501,990 | 63.9 ± 2.0 | 498,499 | 75.1 ± 4.2* |
| 31–50 y | 1,426,388 | 65.7 ± 1.2 | 1,795,207 | 80.2 ± 1.7* |
| 51–70 y | 1,469,586 | 69.6 ± 0.9 | 2,410,181 | 83.9 ± 1.2* |
| ≥71 y | 615,113 | 68.4 ± 1.2 | 983,308 | 82.2 ± 1.0* |
| Males | ||||
| 9–13 y | 259,155 | 54.1 ± 1.4 | 263,043 | 63.3 ± 2.1* |
| 14–18 y | 151,808 | 54.9 ± 2.2 | 158,099 | 66.0 ± 3.1* |
| 19–30 y | 495,112 | 57.3 ± 2.7 | 475,066 | 72.6 ± 6.2* |
| 31–50 y | 908,543 | 60.4 ± 1.8 | 1,196,276 | 80.2 ± 2.4* |
| 51–70 y | 865,797 | 61.8 ± 1.7 | 1,292,140 | 79.1 ± 1.6* |
| ≥71 y | 300,747 | 63.5 ± 1.6 | 535,580 | 79.5 ± 2.0* |
| All participants | 8,451,866 | 63.2 ± 0.5 | 11,232,024 | 78.1 ± 0.6* |
Values are presented as mean of percentages ± SE and analysis was conducted separately for 2004 and 2015 data sets (18, 19).
The total n for children 1–3 y and 4–8 y.
Significant differences (P < 0.05) in % contributions between 2004 and 2015 by age groups with use of confidence interval overlap technique (22).
Prevalence of vitamin D supplement use in 2004 and 2015
From 2004 to 2015, the prevalence of vitamin D supplement use increased in all but 1 age group (children aged 1–8 y), as shown in Figure 1. Overall, the percentage of vitamin D supplement users in the Canadian population significantly increased (P < 0.05) from 28.1% in 2004 to 33.1% in 2015.
FIGURE 1.
Prevalence of vitamin D supplement use in 2004 and 2015 across age-specific and sex-specific groups among Canadians. Values are represented as percentages ± SE (18, 19). Analyses were conducted separately for 2004 and 2015 data sets. *Significant difference (P < 0.05) in supplement users between 2004 and 2015 by age/sex groups with use of CI overlap technique (22). CCHS 2004: n = 8,451,866, CCHS 2015: n = 11,232,024. C, children; CCHS, Canadian Community Health Survey; F, females; M, males.
Factors associated with vitamin D supplement use in 2004 and 2015
Factors associated with vitamin D supplement use in 2004 and 2015 are listed in Table 4. The odds of taking a vitamin D supplement were 3.9 times greater among children aged 1–8 y than males aged 14–18 y (as the reference group with the lowest intake) in 2004. Older age and being female were also associated with higher odds of vitamin D supplement use. In 2015, the odds of vitamin D supplement use were 2.3 times and 4.9 times greater among men and women aged ≥71 y than men aged 19–30 y (reference group), respectively. Among Canadians, having a university degree was associated with higher odds of vitamin D supplement use than those without university education in 2004 (OR: 1.3; 95% CI: 1.1, 1.4) and 2015 (OR: 1.2; 95% CI: 1.02, 1.4). Being food secure was associated with higher odds of taking a vitamin D supplement in 2015 (OR: 1.3; 95% CI: 1.02, 1.6), but not in 2004. In 2015, living in urban areas was associated with 1.5 times (95% CI: 1.2–1.8) higher odds of vitamin D supplement use when compared with rural areas. However, this association was not observed in 2004. Compared with Canadians in lower-income deciles, Canadians in higher-income deciles had 1.3 times (95% CI: 1.2–1.4) and 1.4 times (95% CI: 1.2–1.6) higher odds of taking vitamin D supplements in 2004 and 2015, respectively. Having reported a chronic condition was not associated with higher odds of taking a vitamin D supplement in both 2004 and 2015 (Table 4).
TABLE 4.
Factors associated with vitamin D supplement use across age and sex groups of Canadians in 2004 and 20151
| 2004 | 20152 | |||
|---|---|---|---|---|
| (n = 8,451,866) | (n = 11,232,024) | |||
| Sociodemographic variables | n | OR (95% CI) | n | OR (95% CI) |
| Age and sex groups | ||||
| All children 1–8 y3 | 1,063,185 | 3.9* (3.2, 4.9) | 1,179,813 | — |
| Male, 9–13 y | 259,155 | 2.1* (1.6, 2.7) | 263,043 | — |
| Female, 9–13 y | 228,140 | 1.9* (1.4, 2.5) | 250,956 | — |
| Male, 14–18 y4 | 151,808 | 1 | 158,099 | — |
| Female, 14–18 y | 166,302 | 1.2 (0.8, 1.6) | 193,856 | — |
| Male 19–30 y5 | 495,112 | 1.5* (1.1, 1.9) | 475,066 | 1 |
| Female, 19–30 y | 501,990 | 1.7* (1.3, 2.3) | 498,499 | 1.4* (0.9, 2.3) |
| Male, 31–50 y | 908,543 | 1.4* (1.03, 1.8) | 1,196,276 | 1.2* (0.7, 1.7) |
| Female, 31–50 y | 1,426,388 | 2.7* (2.1, 3.4) | 1,795,207 | 2.1* (1.4, 3.2) |
| Male, 51–70 y | 865,797 | 2.3* (1.8, 2.9) | 1,292,140 | 1.6* (1.03, 2.4) |
| Female, 51–70 y | 1,469,586 | 5.0* (3.9, 6.4) | 2,410,181 | 4.4* (2.9, 6.5) |
| Male, ≥71 y | 300,747 | 2.5* (1.8, 3.4) | 535,580 | 2.3* (1.5, 3.6) |
| Female, ≥71 y | 615,113 | 5.1* (3.8, 6.7) | 983,308 | 4.9* (3.2, 7.5) |
| Education6, * | ||||
| No university degree7 | 5,458,383 | 1 | 6,440,471 | 1 |
| A university degree | 2,878,036 | 1.3* (1.1, 1.4) | 4,788,629 | 1.2* (1.02, 1.4) |
| Food security status8, * | ||||
| Insecure7 | 945,573 | 1 | 1,073,389 | 1 |
| Secure | 7,490,648 | 1.01 (0.9, 1.2) | 10,128,567 | 1.3* (1.02, 1.6) |
| Area of residence9, † | ||||
| Rural7 | 1,403,945 | 1 | 1,683,026 | 1 |
| Urban | 7,047,919 | 1.1 (0.9, 1.3) | 9,548,998 | 1.5* (1.2, 1.8) |
| Income deciles10, † | ||||
| Decile 1–57 | 3,456,691 | 1 | 5,193,746 | 1 |
| Decile 6–10 | 4,287,972 | 1.3* (1.2, 1.4) | 6,038,278 | 1.4* (1.2, 1.6) |
| Chronic condition11, † | ||||
| No7 | 6,579,616 | 1 | 5,991,022 | 1 |
| Yes | 1,870,993 | 1.03 (0.9, 1.2) | 3,192,802 | 1.2 (0.9, 1.4) |
Values are presented as ORs (95% CI) and analysis was conducted separately for 2004 and 2015 data sets (18, 19).
Missing ORs for some DRI age groups in 2015 are a result of missing information on chronic conditions (used as covariate for logistic regression) for children and adolescents aged <19 y.
The DRI age groups of children aged 1–3 y and 4–8 y were merged and data presented for the age group 1–8 y.
Reference group for OR comparison in 2004.
Reference group for OR comparison in 2015.
Yes: If any household reported having a university degree and No: If any household reported having less than a university degree.
Reference group.
Yes: If any individual reported food secured and No: If any individual reported marginal, moderate, or severe food insecurity.
Urban: If any individual reported living in urban areas and Rural: if any individual reported living in rural areas.
Income decile 1–5: If any individuals reported having income in decile 1, 2, 3, 4, or 5 and income decile 6–10: If any individuals reported having income in decile 6, 7, 8, 9, or 10.
Yes: If an individual had reported having any of the following diseases: diabetes, heart disease, cancer, osteoporosis, and hypertension and No: If an individual did not report having diabetes, heart disease, cancer, osteoporosis, or hypertension.
Significant difference within categories when P value < 0.05.
The total n might vary in sociodemographic variables (education, food security, area of residence, income deciles, and chronic condition) because of missing values.
Discussion
This is the first study to report trends in dietary and total usual vitamin D intake in Canada between 2004 and 2015, through use of nationally representative samples. Overall, the usual intake of vitamin D from the diet decreased from 2004 to 2015 in vitamin D supplement nonusers by 1 μg/d; however, no statistically significant decrease was observed in vitamin D supplement users. The drop in dietary vitamin D intake may be explained by a decrease in the contribution of the “Milk and Alternatives” food group to usual dietary vitamin D intake that was significantly lower in 2015 than in 2004 among both vitamin D supplement users and nonusers. From 2004 to 2015, the percentage contribution of supplemental vitamin D to daily vitamin D intake increased across all age and sex groups in vitamin D supplement users. The percentage of Canadians taking a vitamin D supplement also significantly increased, from 28.1% in 2004 to 33.1% in 2015. Between 2004 and 2015, the prevalence of vitamin D inadequacy significantly increased among Canadian vitamin D supplement nonusers; however, among users of vitamin D supplements, the prevalence of vitamin D inadequacy significantly decreased.
Despite the development of current DRIs in 2011 that increased the RDA for vitamin D for Canadians and Americans aged 1–70 y from 5 μg/d to 15 μg/d (5), there has been no significant improvement in dietary intake of vitamin D in Canada and the United States in recent years. From 2004 to 2015, overall vitamin D intake from foods significantly decreased in vitamin D supplement nonusers aged ≥1 y (from 5.2 μg/d to 4.2 μg/d). Consistent with our findings, Harnack et al., through use of data from the Minnesota Heart Survey, showed that vitamin D intake from food sources decreased in both American men (from 7.2 μg/d to 6.1 μg/d) and women (from 4.7 μg/d to 4.5 μg/d) aged 25–74 y between 1980–1982 and 2007–2009 (27). In parallel, results from the cross-sectional NHANES revealed that age-standardized mean 25-hydroxyvitamin D [25(OH)D] concentrations in vitamin D supplement nonusers (aged ≥12 y) decreased from 60 nmol/L in 1988–1994 to 57 nmol/L in 2005–2006 (28). However, during the same time, the mean 25(OH)D concentrations remained unchanged in the overall US population, which appeared to be related to vitamin D supplement use (28). Recent estimates from NHANES also demonstrated that the mean daily intake of dietary vitamin D decreased from 5.3 μg/d in 2009–2010 to 4.8 μg/d in 2015–2016 among Americans aged ≥2 y (29, 30). Low dietary vitamin D intake is reflected in 25(OH)D blood concentrations of Canadians (31). The EAR was set to maintain 25(OH)D at or above 40 nmol/L, and for Canadians in winter who did not report supplement use, 20.9% were below this concentration (31), thus indicating low biomarker amounts when sun exposure was at a minimum. This downward trend in vitamin D intake from food sources may exacerbate the problem of vitamin D insufficiency/deficiency among communities. Although in Canada, food companies have to provide a Nutrition Facts table on their prepackaged foods, providing information on the amount of vitamin D is not mandatory (32). Because food label reading is a common behavior among Canadian adults (33), providing vitamin D information on the Nutrient Facts table may help consumers to make better food choices in terms of vitamin D content and may prompt more companies to fortify their foods.
Our results revealed that the “Milk and Alternatives” food group remains the most important source of vitamin D intake among Canadians in 2015, as we reported for 2004 (9). In 2015, “Milk and Alternatives” contributed >35% of the usual dietary intake from foods. Yet the downward trends observed in vitamin D intake from food sources among Canadians and Americans may be attributable to the general tendency toward decreasing consumption of dairy products (34, 35). In support of this, we showed that between 2004 and 2015, the contribution of the “Milk and Alternatives” food group to usual dietary vitamin D intake significantly decreased by 5.8% in vitamin D supplement nonusers and by 7.1% in vitamin D supplement users. Similarly, the proportion of vitamin D intake from milk and milk drinks among US adults decreased from 48.2% in 2003–2006 to 39.2% in 2007–2010 (36, 37). In line with this, a report of trends in consumption of dairy products in the United States demonstrated that between 1970 and 2012, the total mass of dairy products available to consume fell from 339 pounds (154 kg) per person per year to 276 pounds (125 kg) per person, which mostly resulted from the decline in milk consumption (34). A similar trend was observed in Finland, where, from 1950 to 2006, the overall consumption of milk decreased and shifted from whole milk to reduced-fat and skim milk (35). The growing popularity of veganism (38, 39) and the cultural habits and high prevalence of lactose intolerance among ethnic subgroups (40) are potential barriers to the consumption of dairy foods. Despite the observed downward trend in consumption of dairy products, the new Canada's Food Guide has eliminated the “Milk and Alternatives” food category and recommended only lower-fat dairy products as a subgroup of protein foods (41). This may accelerate this downward trend and thereby reduce the dietary intake of vitamin D even further, despite the plan to double the amount of vitamin D in fluid milk by 2023 (42).
From 2004 to 2015, significant increases in the proportion of vitamin D obtained from “Grain Products,” “Enriched Beverages,” and “Other Foods and Beverages” categories partly compensated the decrease in the contribution from the “Milk and Alternatives” food group, especially among vitamin D supplement users. Among the Canadian population, the “Meat and Alternatives” food group was the second leading contributor to dietary vitamin D intake, followed by “Other Foods and Beverages” (including oils and fats), “Grain Products,” “Enriched Beverages,” and “Vegetables and Fruit.” Similarly, in a study conducted in Canadian-born Chinese people, milk contributed the largest amount of vitamin D to the diets (49.3%). Other vitamin D sources included fatty fish (12.5%), red meats (11.1%), butter/margarine (5.3%), eggs (4.8%), and mushrooms (4.0%) (43). Similar to Canadians, milk/milk products were the major dietary sources of vitamin D among Americans, providing 43.7% of the dietary intake. Meats and fish (25.8%) were other important sources of vitamin D, followed by grains (12.2%), eggs (9.5%), and fruit and juices (2.8%) (36). In countries with no mandatory fortification of milk, the major contributors to vitamin D intake among an Irish adult population aged 18–64 y were meat/meat products (30.1%), fish (14.3%), and eggs (9.1%) (44), and the main sources of dietary vitamin D in a sample of independently living German elderly were fish/fish products (40%), followed by eggs, fats/oils, bread/bakery products, and milk/dairy products (45). Further, it has been shown that fish are major contributors to vitamin D intake in East Asian countries with low milk consumption, such as Korea and Japan (46, 47).
Our results showed that both the prevalence of vitamin D supplement use and the percentage contribution of supplemental sources to daily vitamin D intake significantly increased between 2004 and 2015. Similar to our findings, the prevalence of daily supplemental vitamin D use of ≥25 μg (1000 IU) significantly increased among US adults aged ≥20 y from 0.3% in 1999–2000 to 18.2% in 2013–2014. Moreover, from 2007 to 2014, the prevalence of daily supplemental vitamin D intake of 4000 IU or more (above the UL) significantly increased from 0.2% to 3.2% (48). In parallel, the prevalence of the US population at risk of vitamin D inadequacy (30–49 nmol/L) decreased from 21% to 17.7%, from 2003 to 2004 through 2013 to 2014 (49). With use of data from 2 large prospective cohorts, Kim and colleagues found that the proportions of health professionals taking a vitamin D supplement also substantially increased in the United States from 1990 to 2006 (50). This upward trend in the prevalence of vitamin D supplement use and the parallel increase in doses of supplemental vitamin D intake may stem from the growing evidence on health-promoting and beneficial effects of vitamin D on both skeletal and nonskeletal outcomes (12–17).
In the current analysis, female sex, older age, higher income, higher education level, being food secure, and residence in urban areas were significantly associated with higher odds of vitamin D supplement use. However, we found no significant association between having a chronic condition and odds of supplement use. With use of data from the 2007–2009 Canadian Health Measures Survey, we previously showed that about 31% of Canadians aged 6–79 y reported taking a vitamin D supplement, of whom near 60% were female. For both males and females, greater supplement use was associated with older age and higher income, but not a higher education level. Moreover, odds of vitamin D supplement use were higher for females reporting ≥1 chronic disease, but not for males (51). Munasinghe and colleagues also reported that Canadian children (10–11 y) who resided in a metropolitan area or whose parents completed college were more likely to be vitamin D supplement users (52). Data from the 2007–2010 NHANES showed that females and participants with higher income were more likely to take vitamin D supplements than males and those with lower income (36). In another study conducted in 8024 South Asians aged 40–69 y living in the United Kingdom, a lower vitamin D supplement usage was observed in males, younger persons, and those living outside Greater London. The authors found a positive association between household income and the odds of vitamin D supplement use (53). These results clearly suggest that certain groups of people are not benefiting from vitamin D supplements.
Because of a decline in dietary vitamin D intake, the prevalence of inadequacy significantly increased among vitamin D supplement nonusers (from 91.9% to 96.5%). However, the increase in the contribution of supplements to daily vitamin D intake resulted in a notable decrease in the prevalence of inadequacy among supplement users (from 20.6% to 14.1%). Hill et al. (54) conducted a study in 7837 US Americans and 4025 Canadians in 2012 and found that <2% of participants in all age groups met the 2011 RDA for vitamin D from foods. In a study conducted in a northern Canadian Dené First Nation community (2013), Slater et al. (55) reported that only 11.1% and 13.0% of the adult participants met the vitamin D 2011 RDA values in winter and summer, respectively. A recent study assessing the adequacy of vitamin D intake among Albertan children showed that about 45% of participants met the EAR for vitamin D. However, when vitamin D intake from diet alone was considered, only 16% met the EAR (56). Although supplement use was accompanied by a considerably lower prevalence of vitamin D inadequacy, not all vitamin D supplement users attained the recommended amount. However, through use of data from cycle 1 of the Canadian Health Measures Survey, we previously showed that use of vitamin D supplements is associated with a better 25(OH)D status among Canadians (31). Therefore, recommendations for supplement use as well as enhanced food fortification programs may help to achieve optimal vitamin D status in the majority of the population.
The primary strength of this study was the use of data from 2 nationally representative surveys of the Canadian population, CCHS 2004 (Cycle 2.2) survey and CCHS Nutrition 2015 survey. One of the major strengths of our study was the opportunity to examine the trends in vitamin D intake (dietary and total) during an 11-y period, in the light of recent evidence on the health-promoting effects of vitamin D. We also acknowledge some limitations. First, because we used data from 2 cross-sectional surveys, this provides only 2 snapshots at 2 different points in time, and thus no causal direction can be established. Second, in 2004, the information regarding vitamin D supplements was available for the previous 30 d, whereas in 2015, the information was collected in the previous 24 h. Third, because changes to the food booklet resulted in some portion size changes, especially in the case of beverages, caution should be used when comparing 2004 and 2015 results. For example, changes to the food portion size booklet resulted in a decrease of 39 mL (429 mL in 2004 to 390 mL in 2015) and 55 mL (325 mL in 2004 to 270 mL in 2015) in quantities of the 2 largest drinking glass options (57). This may have an impact on under-reporting the amount of vitamin D intake in CCHS 2015, although the difference in portion size translates to between 0.39 and 0.55 μg/d. Fourth, because the 2004 and 2015 data were analyzed separately, the comparisons were made by a 95% CI overlapping method. Fifth, the EAR for vitamin D is the daily intake needed to meet the requirements of half the healthy individuals and does not reflect any influence of sun exposure, which could mean that some individuals do not need to intake the full EAR. Lastly, dietary vitamin D intake was assessed with 24-h recall, which is a self-report method subject to misreporting (i.e., overestimating or underestimating dietary intake).
In conclusion, we used 2 nationally representative surveys conducted in 2004 and 2015 to examine the trends in dietary and total vitamin D intake among Canadians. From 2004 to 2015, dietary vitamin D intake of Canadians significantly decreased, especially among supplement nonusers. This may be attributable to the parallel decrease in the proportion of dietary vitamin D provided by the “Milk and Alternatives” food group, as a major contributor to vitamin D intake. During these 11 y, the prevalence of vitamin D supplement use significantly increased among Canadians. The percentage contribution of supplemental sources of vitamin D to daily vitamin D intake also increased among all age and sex groups. The decreasing trend in the intake of vitamin D from food sources should be taken into consideration in efforts to decrease the high prevalence of vitamin D insufficiency/deficiency. In 2015, a high proportion of vitamin D (about 45% in vitamin D supplement nonusers and near 35% in vitamin D supplement users) came from fortified milk. Canada has initiated plans to double the amount of vitamin D in fluid milk by 2023, which will result in a lower prevalence of vitamin D inadequacy. Further, because of the limited availability of dietary sources, it is apparent that there should be an emphasis on taking vitamin D supplements to maintain appropriate serum vitamin D concentration among Canadians (8), especially in winter.
ACKNOWLEDGEMENTS
The authors’ responsibilities were as follows—HV and SJW: design of the study; NI and HV: formal analysis; HV, SJW, MS, NI, and RPP: original draft preparation; HV and SJW: editing and review of the manuscript; and all authors: read and approved the final manuscript. Osteoporosis Canada is the collaborating partner for knowledge translation initiatives resulting from this study.
Notes
Supported by Canadian Institutes of Health Research (grant no. 418774).
Author disclosures: The authors report no conflicts of interest.
Abbreviations used: CCHS, Canadian Community Health Survey; EAR, estimated average requirement; IOM, Institute of Medicine; NCI, National Cancer Institute; UL, tolerable upper intake level; 25(OH)D, 25-hydroxyvitamin D.
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