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. Author manuscript; available in PMC: 2015 Aug 21.
Published in final edited form as: P R Health Sci J. 2015 Jun;34(2):83–88.

Prevalence of vitamin D insufficiency and deficiency among medical residents of the University Hospital in San Juan, Puerto Rico

Leticia Hernández Dávila 1, Nixzaliz Rodríguez Rivera 1, Mariel López Valentin 2, Lillian Haddock 1, Renil Rodríguez Martínez 3, Alex González Bossolo 3, Margarita Ramírez Vick 1,✉
PMCID: PMC4544697  NIHMSID: NIHMS713943  PMID: 26061058

Abstract

Vitamin D has been attracting increased attention due to higher prevalence of vitamin D insufficiency and deficiency than expected in areas with sufficient sun exposure. Even though sunlight exposure and diet are the main determinants of Vitamin D status, other factors such as: age, race, use of sunscreen, medications, and malabsorptive conditions affect vitamin D levels.

Recent studies have found a high prevalence of vitamin D deficiency and insufficiency in different populations. However, there is limited data of the prevalence of vitamin D deficiency and insufficiency in Puerto Rico. To answer that question we evaluated a sample of 51 internal medicine residents from ages 25 to 39 of the University Hospital in San Juan, Puerto Rico by means of a questionnaire about basic socio-demographic characteristics, anthropometric data, and lifestyle characteristics and obtained blood sampling for 25-hydroxyvitamin D levels.

The median 25-hydroxyvitamin D level was 21 ng/mL (range, 7–38 ng/mL). Forty-five participants (88.2%) had 25 hydroxyvitamin D concentrations <30 ng/mL. We found vitamin D deficiency in 43.1% of the population and insufficiency in 45.1%.

Contributory factors to our findings include limited exposure to sunlight during the periods of higher sun intensity, increased body mass index and a limited area of body exposed to sunlight. A relationship between lower physical activity levels and hypovitaminosis D was also found. Both calcium intake and vitamin D intake, which were markedly below recommended daily allowance, were positively correlated with 25-hydroxy vitamin D levels, but with a weak association.

Indexing Terms: 25-Hydroxyvitamin D, Calcium, dietary, Vitamin D, dietary, Sunlight exposure, Physical Activity

INTRODUCTION

Cholecalciferol is a pro-hormone synthesized in the skin after ultraviolet radiation exposure (80–90%) or obtained in diet to a lesser extent. This pro-hormone is metabolized in the liver to 25-hydroxyvitamin D and then further metabolized in the kidneys to 1, 25-dyhydroxyvitamin D which is the metabolic active form of Vitamin D. Even though sunlight exposure and diet are the main determinants of Vitamin D status, other factors such as: age, race, use of sunscreen, medications, and malabsorptive conditions affect vitamin D levels.

During recent years, vitamin D has been attracting increased attention due to higher prevalence of vitamin D insufficiency and deficiency than expected in areas with sufficient sun exposure. [1–7] Vitamin D is an essential hormone and vitamin in the human body with a variety of actions, including: regulation of body calcium and phosphate levels and bone mineralization. This hormone has also been related to risk of metabolic syndrome, obesity, insulin sensitivity, diabetic retinopathy, adverse obstetric and newborn outcomes, cardiovascular health, and all cause mortality. [8–16] Current literature has suggested that vitamin D supplementation may have a role in improving several chronic conditions aside from the proven effect on bone mineral density and fracture reduction. [17–22] However, other studies have not been able to prove this therapeutic effect. [23]

Many studies have evaluated the prevalence of hypovitaminosis D in different populations. [1–7] According to the Third National Health and Nutrition Examination Survey (NHANES), the prevalence of vitamin D deficiency in adults in the United States has been reported to be 25–75%. [24] On the other hand, there is scant information regarding the prevalence of Vitamin D deficiency or insufficiency in healthy persons living in Puerto Rico. It is important to evaluate the prevalence of hypovitaminosis D in our population, since a higher than expected prevalence of low vitamin D levels has been found in areas with abundant sunlight availability.

Young physicians during their training years would be expected to be especially vulnerable to vitamin D insufficiency due to their long indoor working hours. Vitamin D levels were obtained in five residents of the University Hospital as part of their annual physical examination and all of them had low vitamin D levels (L.Hernández, personal communication, May 2010). This finding and the lack of data on vitamin D status in medical residents raised the concern that vitamin D insufficiency may be more common than expected among Puerto Rican residents, despite living in a tropical area. To answer that question we designed a research study to estimate the prevalence of vitamin D insufficiency and deficiency in residents of the University Hospital in San Juan, Puerto Rico. The aims of this study were to: 1) assess the prevalence of Vitamin D deficiency or insufficiency among residents of different specialties of the University Hospital of San Juan Puerto Rico; 2) investigate the different factors that could influence the prevalence of hypovitaminosis D among said population.

MATERIAL AND METHODS

Target Population

The target population was composed of residents from the Internal Medicine Program and subspecialties of the University Hospital. Exclusion criteria included: chronic renal insufficiency (creatinine levels >1.5 mg/dL), chronic liver disease (bilirubin levels >2 mg/dL) and malignancies. A total of 100 residents were invited to participate in this study: residents of Internal Medicine Program (49), residents of internal medicine subspecialties of the University Hospital (47) and four research fellows. The participation rate was 51% (51/100).

Data Collection

The residents were invited to fill in the study questionnaire and undergo blood sampling for 25-hydroxyvitamin D, and other biochemical parameters. Blood samplings were obtained through the Intensive Cooperative Laboratory of the University Hospital. Previous laboratory results (no more than 6 months) were considered in this study, as well. These procedures took place at the date determined either by the program director or the chief resident of each program. Blood samples for 25OHvitamin D levels were taken mainly during two seasons of the year, spring (March–May) and winter (November–January). Both interventions were done after obtaining oral informed consent to participate in the study. Study procedures were approved by the Institutional Review Board of the University of Puerto Rico, Medical Sciences Campus.

Questionnaire Information

The questionnaire included questions about basic socio-demographic characteristics, anthropometric data, physical activity, diet, sun exposure, and working hours. Body mass Index was categorized according to the World Health Organization definition: Normal (18.5 kg/m2–24.9 kg/m2) and Overweight (≥25 kg/m2). Daily dietary intake of calcium and vitamin D were calculated from the data obtained from a food frequency questionnaire (FFQ) containing 24 questions focusing on both calcium and vitamin D-containing foods consumed regularly. This FFQ was developed for the Latin American Vertebral Osteoporosis Study [25] and validated for the Puerto Rican population by Suárez E and Pérez C, 2009. Current vitamin and mineral supplementation open-ended question was included and used for calculation of mean total intake. To assess the frequency of each food there were 8 choices that ranged from ‘3 or more servings per day’ to ‘rarely or never’. Total intakes of vitamin D and calcium were determined by adding calcium and vitamin D content of food items according to the Department of Agriculture National Nutrient Database for Standard Reference, 2011. Physical activity was categorized as: (1) no physical activity, (2) less than 2.5 hours per day, and (3) 2.5 hours or more per day. Sun exposure was expressed as: (1) Low (not between 10:00 am to 4:00 pm), and (2) High exposure (between 10:00 am and 4:00 pm). Working hours were reported by participants in answer to a question asking the number of hours worked per day (1) ≤9 hours per day and (2) >9 hours per day. In order to estimate the percentage of body surface area exposed to the sun, a total body surface area calculator diagram was used (Wallace, 1951, Rules of Nine Chart).

Biochemical Analysis

Serum 25-hydroxyvitamin D levels were determined using liquid chromatography-tandem mass spectrometry at a reference laboratory, Quest Diagnostics-Tampa, Fl. According to the US Institute of Medicine [26], a 25-hydroxyvitamin D level above 20ng/mL can be considered sufficient at least for skeletal health. And, in recent years, several authors have considered a value above 30ng/mL to be optimal for prevention of many extraskeletal conditions. Therefore, in our study, 25-hydroxyvitamin D levels were categorized as: (1) Deficiency (<20ng/mL, <50 nmol/L), (2) Insufficiency (20–29 ng/mL, 50–74 nmol/L), and (3) Sufficiency (≥ 30 ng/mL, ≥75 nmol/L).

Statistical Analysis

Normally distributed data was summarized as means with respective standard deviations, and non-normally distributed data were presented as medians, with its respective percentiles (P25, P75). Comparison of proportions and means between circulating levels of serum 25-hydroxyvitamin D [25(OH)D] groups were based on Fisher Exact/Pearson Chi-square test and ANOVA, respectively; medians were compared with the use of Kruskal-Wallis equality-of-populations rank test. Spearman rank correlations were performed to assess association between total daily vitamin D and Calcium consumption with 25-hydroxyvitamin D. For all tests a p value <0.05 was considered statistically significant. Statistical analysis was performed using the STATA software v. 11.2.

RESULTS

Characteristics of the study group

A total of 51 Hispanic residents participated in this study (Table1). The study sample consisted of 45.1% women and 54.9% men, both of which were evenly distributed among the postgraduate training programs (49.0% PGY1-PGY2 and 51.0% PGY3 or higher). Women had a median age of 30 years old (range, 26–39) and average Body Mass Index (BMI) of 23.7 kg/m2. Men had a median age of 28 years old (range, 25–34) and average BMI of 27.0 kg/m2. Seventy-eight percent of the male residents were classified in overweight category versus twenty-six percent of the women. Thirty (59%) of the participants considered themselves of mixed race, 16 (31%) white, 4 black, and one asiatic.

Table 1.

Anthropometric characteristics of a sample of 51 internal medicine residents of the University Hospital, San Juan, Puerto Rico according to circulating 25(OH) Vitamin D levels.

Overall Sample (n=51) Deficient or less than 20 ng/mL (n=22, 43%) Insufficient or 20–29 ng/mL (n=23, 45%) Sufficient or ≥30 ng/mL (n=6, 11%) P value
Sex (%)
 Female 45.1 54.6 34.8 50.0 0.42
 Male 54.9 45.5 65.2 50.0
Mean Age (yrs.)† 29.1 (±2.9) 28.9 (±2.2) 29.6 (±3.6) 28.3(±2.3) 0.58
Mean BMI (kg/m2) † 25.5 (±3.9) 25.3 (±4.0) 26.5 (±3.7) 22.3 (±2.3) 0.05***
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†

Normally distributed data reported as Mean (± SD)

***

P value < 0.05

Health behaviors

More than half of the participants (51.0%) performed less than 2.5 hours per week of physical activity. Only 13.7% of participants reported being exposed to the sun between 10:00 am and 4:00 pm. The median percentage of body area exposed to sun was 13.5%. The total daily calcium consumption and vitamin D medians were 303.7 mg (P25 =148.13mg, P75= 652 mg) and 133.3 units (P25 = 49.5 units, P75= 241.6 units), respectively. (Table 2)

Table 2.

Lifestyle characteristics of sample of 51 internal medicine residents of the University Hospital, San Juan, Puerto Rico according to circulating levels of 25(OH) Vitamin D.

Characteristic: Overall Sample (n=51) Deficient or < 20 ng/mL (n=22) Insufficient or 20–29 ng/mL (n=23) Sufficient or ≥30 ng/mL (n=6) P value
Tobacco use (%)
 None 72.0 81.8 60.9 80.0 0.27
 Former and Current Smokers 28.0 18.2 39.1 20.0
Physical Activity (%)
 None 19.6 36.4 4.4 16.7 0.03***
 Less than 2.5 hours/week 51.0 27.3 69.6 66.7
 2.5 or more hours/week 29.4 36.4 26.1 16.7
Dietary habits††
 Total daily calcium consumption (mg) 303.1 (148.1, 652.0) 234.5 (122.4, 280.5) 515.2 (323.2, 722.1) 255.1 (68.1, 409.9) 0.01***
 Total Vitamin D consumption (Units) 133.3 (49.5, 241.6) 103.9 (42.5, 145.5) 159.3 (68.2, 261.1) 78.2 (16.0, 274.5) 0.33
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††

Non-normally distributed data reported as Median (P25, P75)

***

P value < 0.05

Serum Values

The median 25-hydroxyvitamin D level was 21 ng/mL (range, 7–38 ng/mL). Forty-five participants (88.2%) had 25 hydroxyvitamin D concentrations <30 ng/mL, 22 (43%) were deficient (<20ng/ml) and 23 (45%) had insufficient levels (20–29 ng/ml).

Bivariate analysis

Twenty five-hydroxyvitamin D concentration was significantly associated with physical activity (p-value <0.05) and Body Mass Index (BMI) (p value<0.05). Mean values of BMI were significantly (P<0.05) higher among individuals with insufficient and deficient levels of 25-hydroxyvitamin D concentration (Table 1). Residents with normal BMI were more prone to have sufficient levels of 25-hydroxyvitamin D concentration (21.7%), compared to those who were overweight (3.6%). Vitamin D deficiency was more common among residents who did not dedicate time for physical activity. Participants who did not report being exposed to sunlight in the period between 10:00 am and 4:00 pm were more likely to have deficient levels of 25-hydroxyvitamin D (<20 ng/mL), compared to those who did (47.7% vs. 14.3%, respectively).

Mean values of total daily calcium consumption were significantly (p<0.05) lower among individuals with deficient levels of 25-hydroxyvitamin D. (Table 2). A significant positive, but weak correlation was found between 25-hydroxyvitamin D concentration and total daily calcium consumption. As total daily Calcium consumption increased, 25-hydroxyvitamin D concentration increased (Spearman’s Coefficient of Correlation = 0.28). There was a positive but weak correlation between 25-hydroxyvitamin D concentration and total daily vitamin D consumption. As total daily vitamin D consumption increased, 25-hydroxyvitamin D concentration increased as well (Spearman’s Coefficient of Correlation = 0.05). Among the few residents (n=7) taking vitamin supplements that included vitamin D, only 43% had sufficient levels.

Although a higher percentage of women had vitamin D deficiency, this was not significant. Neither gender nor age was found to be significantly different among the groups. Self-reported race was not associated to vitamin D status (p value 0.17), nor was season (p value 0.85) of blood sampling (data not shown). Age, working hours, 24hr on-duty call, smoking and years of residency were not found to be contributing factors to 25-hydroxyvitamin D concentration.

Discussion

The purpose of the present study was to estimate the prevalence of 25-hydroxyvitamin D deficiency and insufficiency in a group of Hispanic resident physicians living in a tropical country. We found that 88.2% of the participants had hypovitaminosis D (43.1% had deficiency and 45.1% had insufficiency). The median 25-hydroxyvitamin D level for the sample was 21 ng/mL (P25=15 ng/mL, P75=27ng/mL).

To our knowledge there is scarce research on vitamin D status in this particular population, though our findings are consistent with other studies on young physicians. Mendoza et al. studied a similar population of Hispanic medical residents and found a 75% prevalence of vitamin D deficiency compared to 45% in a matched-control group. [27] In another group of medical residents living in a tropical region of India, Singh et al. found a 98% prevalence of hypovitaminosis D. [28] Our group of young physicians compares with these similar populations in this respect.

Moreover, concerning other populations in Puerto Rico, Suárez-Martínez EB et al. found in over 4,000 Puerto Ricans island-wide, hypovitaminosis D (<30 ng/mL) in 68.5% of subjects[29]; while Palacios C et al. found in a sample of overweight/obese adults in Puerto Rico a 45% prevalence of vitamin D insufficiency and a median serum 25-hydroxyvitamin D level of 30.7 ng/mL.[30] Also, among Hispanics living in the United States, NHANES III data showed a mean 25-hydroxyvitamin D levels of 27.4 ng/dL for men and 22.71 ng/dL for women. [31] The higher prevalence of hypovitaminosis D found in our sample could be explained by a lesser exposure to sunlight during the periods of higher sun intensity and limited physical activity commonly seen during the residency years of young physicians.

The participants with higher BMI were more likely to have either vitamin D deficiency or insufficiency. An inverse association of adiposity and vitamin D levels has been previously described. [10, 32–33] It is interesting to note that, our group of individuals with sufficient 25-hydroxyvitamin D levels, representing only 11.8% of our population (n=6), had a significantly lower BMI compared to the groups with low vitamin D levels (22.3 vs 25.9 kg/m2), despite having poor calcium and vitamin D intake. This unexpected finding could be due to reporting errors when recalling food intake, or too small a number of people to arrive at any valid conclusion. It is of interest that in this particular sample of young physicians, mean BMI among female residents was normal, while the male population mean was in the overweight range, although no significant difference in vitamin D status per gender was found.

Calcium intake and vitamin D intake were markedly below the recommended daily allowance (See Figures 1 and 2) for the population as a whole. Both calcium intake and vitamin D intake were positively correlated with 25-hydroxy vitamin D levels, but with a weak association. Vitamin D and calcium intake was higher in individuals with insufficient serum 25-hydroxyvitamin D levels when compared to individuals with deficient levels. However, this association was not found in individuals with sufficient levels likely due to a very small number of participants in this group. Excluding this group with sufficient vitamin D from the analysis, makes it even more evident that individuals with insufficient 25-hydroxyvitamin D levels do have significantly better calcium and vitamin D consumption as well as exposure to sun in solar radiation peak hours compared to individuals with deficient levels. Low calcium and vitamin D intake among the US population has been consistent in literature. [6–7, 34–36] But, in this case, the possibility of recall bias and the characteristics of the questionnaire may have had an impact in these results.

Figure 1.

Figure 1

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Daily calcium intake according to 25-OH Vitamin D levels

Figure 2.

Figure 2

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Daily Vitamin D intake according to 25-Hydroxyvitamin D Levels

Among the limitations of the present study we can mention the use of a small convenience sample which limits the application of our findings. Also serum PTH levels and other biomarkers associated with vitamin D metabolism were not measured in our study because our population of apparently healthy young physicians was not expected to have abnormalities in this respect. Another limitation is the use of self-reported race which is not necessarily an accurate measure of skin color.

However, our findings reinforce the possibility of higher prevalence of hypovitaminosis D in our population than expected for a young population living in a tropical country. Also, it raises the concern of dietary and lifestyle aspects contributing to low 25-hydroxyvitamin D levels in an educated cohort. Based on our findings, we suggest implementation of counseling and promotion of healthier lifestyles among young physicians who might be resorting to unhealthy habits due to the high demands of their profession.

Further studies with a larger sample should be done to determine the prevalence of hypovitaminosis D in other groups of professionals working indoors and living in Puerto Rico who might have unsuspected low levels and would benefit from supplementation. The long term implications of low vitamin D levels and benefits of replacement in healthy persons are yet to be determined.

CONCLUSION

We found a high prevalence of hypovitaminosis D in a convenience sample of physicians living in a tropical country. Significant determinants of vitamin D status for our population include: calcium and vitamin D intake, physical activity, body mass index and sun exposure between 10:00am and 4:00 pm.

Acknowledgments

This publication was possible by Grants from the National Center for Research Resources (U54RR026139-01A1) and the National Institute on Minority Health and Health Disparities (8U54MD007587-03). Its content is solely the responsibility of the authors and do not necessarily represent the official view of NIH.

Footnotes

Conflicts of interest: The authors have no conflict of interest to disclose.

Funding sources:

We had no external funding for this work.

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