Skip to main content
PMC home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2005 Oct 17.
Published in final edited form as: Altern Ther Health Med. 2005;11(3):48–53.

PATTERNS OF DIETARY SUPPLEMENT USAGE IN DEMOGRAPHICALLY DIVERSE OLDER PEOPLE

Shirley S Kishiyama 1, Marjorie J Leahy 1, Tracy A Zitzelberger 1, Robin Guariglia 1, Daniel P Zajdel 1, James F Calvert Jr 1, Jeffrey A Kaye 1, Barry S Oken 1
PMCID: PMC1255934  NIHMSID: NIHMS4214  PMID: 15945136

Abstract

Objective

To analyze dietary supplement usage data from 494 older adults, aged 65 to 101 years.

Setting

Community dwellers living independently of institutionalized care.

Design

All dietary supplements, including botanicals, were recorded to aid in assessing the health status of older adults.

Participants

1) 224 individuals enrolled in a study that follows the health of persons 85 years and older (oldest-old) in Klamath County, a non-metropolitan area in southern Oregon: 2) 134 participants of oldest-old age living in the metropolitan Portland area, enrolled in a randomized clinical trial of GBE biloba extract (GBE) for dementia prevention: and 3) 136 participants, ages 65–85 years (young-old), also of the Portland area, enrolled in a study of the effects of yoga and exercise on cognition.

Measurements

Data verified from labels, not from self-report.

Results

Of the participants, 70.6% used dietary supplements. Women took supplements more often than men, and usage decreased with age. A greater percentage, 67.4%, of the non-metropolitan oldest-old took supplements, compared to 56.7% of the metropolitan oldest-old. The greatest usage, 89.7%, was in the metropolitan young-olds. All of these percentages exceed those for comparable age groups in national representative surveys.

Conclusions

Dietary supplement usage by older adults in these studies in Oregon exceeded that in other reports and may reflect high interest in complementary and alternative medicine. This report confirms the results of other studies showing that elderly adults, particularly women, use dietary supplements more than other segments of the US population. Researchers and clinicians should be aware of this pattern and potential conflicts with research design or treatment regimen intended for older people.

Congressional passage of the Dietary Supplement Health and Education Act (DSHEA) in 19941 made a proliferation of products aimed at health improvement possible. Even before 1994, reports had shown dietary supplement usage in the US to be highest in the 65-year-old and older adults,2–5 and now the usage by this older population appears to be increasing.6

This is the first in-depth study of dietary supplement usage among older people in Oregon. These data result from systematically recorded supplement usage in three aging study groups, totaling 494 people. The pooled data allows comparison to other regional, national and international surveys. Combining the 85-year-old and older sub-datasets provides data on 358 oldest-old. Calculations from Census 2000 and 1990 totals indicate the oldest-old group is increasing proportionally faster than any other group after the 45-to-55 year olds.7,8 The data also allow subset comparison between metropolitan and non-metropolitan usage among the oldest-old and comparison between a young-old group of 65-to-85-year-olds and the oldest-old who are living in the same metropolitan area.

The gathering of these data differed from methods described in previous reports on supplement usage in that we recorded every supplement. This allowed for a detailed report rather than one that was limited to selected supplements of epidemiological interest such as antioxidants and their possible links to cancer prevention, or the most popular as established by previous surveys. Our method of individual supplement listings expanded the categories by listing each botanical rather than placing them all into an “others” category. Such a priori categorizations would have precluded detecting new trends of supplement usage and been insensitive to the growth in the supplement industry.

METHODS

One dataset was built by combining the data from three aging studies, one in Klamath Falls, Oregon and two in Portland, Oregon. All three study protocols had institutional review board approval and adhered to the ethical standards set forth in the Helsinki Declaration of 1975.

The Klamath Exceptional Aging Project

In the Klamath Exceptional Aging Project (KEAP), 224 elders aged 85 years and older were recruited by posters, brochures, newspaper advertisements, and community out reach programs. This longitudinal study investigated the normal course of aging and the causes of Alzheimer’s disease. Information about supplement usage was obtained during an intake interview in the home and actual supplement bottles were seen.

The Dementia Prevention Study

In the Dementia Prevention Study (DPS), 134 elders aged 85 and older, were recruited by letters sent to age appropriate persons identified by the Department of Motor Vehicles and Oregon Voter Registration. Supplement usage information was obtained by questionnaire and verified at a home visit. This study was a four-year placebo-controlled trial of GBE, 240 mg per day for prevention of mild cognitive impairment. Individuals who reported use of GBE were asked to stop using the herb for two months and then randomized into the study.

The Effects of Yoga and Exercise on Cognition in Healthy Elders

Healthy elders, ages 65 to 85, recruited by outreach via talks and newsletters to aging community groups to participate in a six-month three-arm randomized trial of yoga, aerobic exercise or wait-list, which was control group that could elect to take an exercise or yoga class as their benefit once they were done with the study. Participants were asked to bring in containers of all medications, vitamins and other supplements on their first, baseline test visit.

The Variables

Six categories of race or ethnicity were used: non-Hispanic white, Asian-American, Hispanic, African-American, Native-American, and other. Education was recorded: first level, 11 years or less; second level, 12 years to 15 years; third level, four or more years of college. In addition to using the continuous value, age was broken in to five-year segments for ease of display and comparison to various other reports with their own arbitrary age categories. We also applied categories to the body mass index (BMI), calculated as weight in kilograms divided by height in meters squared and broken into six ranges: <17, ≥17 to <20, ≥20 to <25, ≥25 to <27, ≥27 to ≤30, and >30.

For discussion purposes, the terms “metropolitan” and “non-metropolitan” were used to refer to the population density differential of the two geographic sites. According to Census 2000 results, 1,444,219 people reside in the 460 square miles comprising the tri-county Portland Metro District, or 3,140 people/sq mile. Klamath County residents number 63,175 in the state’s fourth largest county equal to 6,151 square miles, or 10 people/sq mile.9 The county is noted for forestland, agriculture and Crater Lake National Park.

Identifying the supplements

Separate fields for supplements were created and added as the data indicated more than one individual was taking any one supplement. Several popular multivitamin brands were classed together and specialty combinations, such as those marketed for “heart health” or “high energy,” were also placed in the multivitamin category if the individual did not take a more common one as well. Commercial multivitamins for eye health and bone health were reported frequently and placed in a separate field, but brand names are not used in this paper. Supplements that are often packaged together (eg, glucosamine and chondroitin) were placed in the same field but counted separately if taken as separate pills. Biochemically similar supplements were also placed together (eg, vitamin A and β-carotene or cod liver oil and fish oil). Iron, potassium chloride, and quinine sulfate are not counted as supplements. We feel that taking iron in old age predates the current trend in supplement usage and the knowledge of iron as a pro-oxidant with possibly deleterious central nervous system effects. Potassium and quinine are more representative of an allopathic regimen rather than reflective of current trends of dietary supplement usage.

In addition to itemizing the supplements, the patterns of usage as (1) percentage of participants who used supplements, (2) low, medium or high level of usage, and (3) total number of supplement pills taken by each individual were examined. The levels of supplement usage were arbitrarily set: no = nothing, low = multivitamin only, medium = one single supplement, and high = anything more than a single supplement. We felt that use of a multivitamin was low-level because it does not reflect the more recent focus on single-substance supplement usage, which was then considered medium usage. High usage was anything more than a single supplement.

Statistical Analysis

SPSS statistical software was used for summary descriptive statistics and tests to determine significance of differences between means.10 A correlation table of the variables (ie, data subset group, gender, education level, BMI, age, race and ethnicity, and the three levels of supplement usage) was initially generated to detect overall patterns. The differences between subsets were compared by analysis of variance (ANOVA). Analysis of covariance (ANCOVA) of possibly related factors was performed to isolate the variables that significantly interacted with measures of usage and use of individual supplements. Specifically, because one of the three subsets composed the younger decades of 65 to 85, age related differences were covaried with subset group membership. P values <.05 are considered significant and are noted in the table and charts or if not illustrated, mentioned in the text as actual values expressed to three decimal places.

RESULTS

Demographics are presented in Table1. Comparing the two oldest-old groups, KEAP was older than the DPS group and its education level was lower. All four centenarians belonged to the KEAP group; and because of this small number they were then combined with the lower half-decade making it the 95+ category. The yoga/exercise group has the highest education level.

The patterns of usage of dietary supplements in terms of percent users, level of usage and total supplements for each group and for the total data set are also shown in Table 1. The KEAP group showed higher usage than the DPS study group (ANOVA, P=.042). The yoga/exercise study group showed significantly higher supplement usage in percent users, level and total number of supplements used. Gender and age significantly correlate with all three measures of usage: percent of users, level, and total number of supplements used (ANOVA, gender: P=.00l, P=.000, and P=.003 respectively; and age: all P values <.001) as detailed in Figure 1. BMI did not correlate to usage.

TABLE 1.

Study Group Demographics

KEAP n=224 DPS n=134 YogaExer n=136 Total N=494
Mean Age 89.3±4.3 87.4±2.2 72.4±4.9 84.1±8.3
Women 67.4% 59.7% 75.0% 67.4%
Caucasian 99.6% 97.8% 85.3% 95.1%
Asian American 1.5% 11.8% 3.6%
Hispanic 0.4% 0.7% 0.4%
African American 2.2% 0.6%
Native American 0.7% 0.2%
<12 years education 32.1% 9.0% 2.9% 17.8%
 12 to 15 years 50.9% 61.9% 45.6% 52.4%
 16 years + 17.0% 29.1% 51.5% 29.8%
Mean BMI 25.2±5.0 26.1±3.9 26.7±4.0 25.9±4.5
Use Supplements 67.4% 56.7% 89.7%* 70.6%
Mean Level Used 1.62±1.31 1.47±1.36 2.37±1.02*
Mean Number Used 1.92±2.04 1.7±1.99 3.98±3.26*
Open in a new tab

Number of individuals per category is expressed as percentage. Of the minorities, only Asian Americans are well-represented. Also shown are the usage patterns per group.

*

Indicates significance at <.001, ANOVA. Means are shown with SD.

FIGURE 1.

FIGURE 1

Open in a new tab

Usage patterns of total dataset reflect significant gender difference (ANOVA) and age by half-decade differences (ANCOVA, with subset group as covariate): (A) Percent usage according to age and gender shows that a greater percentage of women use dietary supplements compared to men (P=.003); percent users decline with each half decade (P<.001); (B) level of usage by each half decade declines (P=.002); also significant, those who do use a dietary supplement are using at least a single supplement and one or more others, P= .004; and (C) the mean total number of supplements taken by each age group also decreases by age, data pooled (P<.000).

The percent usage among non-Caucasians was 79.1% compared to 70.2% among Caucasians. Among the groups, the only well-represented minority group was Asian-American, 88.9% of whom used dietary supplements. Their higher level of usage and total number of supplements were significant (ANOVA, P=.011 and .046, respectively.)

A significant correlation between education level, which is highest in the young-old of the yoga/exercise group, and the three measures of usage (P values all <.01) disappeared when only the oldest-old in ANCOVA was performed with group subset as covariate. When the oldest-old data subsets were collapsed, only gender and age remain as significant factors in measures of usage (data not shown).

Multivitamins were the most commonly used dietary supplement, as shown in Figure 2. The order of the 20 most commonly taken supplements after the multivitamin among the 494 total pooled individual records and for each of the three groups is also shown. If the multiple for bone health whose first ingredient is calcium and antacids taken for calcium content were combined with the calcium category, then calcium would be the second most frequently taken supplement before vitamin E, but the difference is not great because many of those who take the other extra source of calcium also take a calcium supplement. The percentages per subset group are also shown because the individual subset group patterns were different. Notably, folate usage is significantly higher in KEAP compared to their urban counterparts, as was a multiple for vision; and in the yoga/exercise study group, ages 65–85, usage of multivitamins, glucosamine/chondroitin, GBE, and B complex was significantly higher than in the other two groups. Usage of the supplements glucosamine and chondroitin, CoQ10, and fish oil were inversely related to age, (P=.013, P<.001, and P=.005 respectively with subset group as covariate). More men than women took lycopene and saw palmetto (ANOVA, P=.042 and P<.001 respectively), and more women than men take calcium (P<.001).

FIGURE 2.

FIGURE 2

Open in a new tab

The supplements are ranked in order of frequency based on the total number of those studied (solid black). The subsets are also shown. Significance of group differences was determined by ANCOVA with age as covariate. P values less than .05 are indicated.

DISCUSSION

The data show very high usage of dietary supplements by older persons, higher than that found in previous US studies,2–5 11–16 and international reports.17–19 Usage rates in the three Oregon studies exceeded those found by the 1999–2000 National Health and Nutrition Examination Survey (NHANES), which shows that 35.9% of respondents of all ages use supplements.20 The high number of supplement usage in this study could be due to increasing usage over the interceding years of the earlier reports, regional character, or both. Although analysts of the National Health Interview Surveys (NHIS) of 1987 and 1992 concluded that dietary supplement usage stabilized,4,5 these surveys only focused on vitamins and minerals, and also predate the current interest in complementary and alternative medicine. Regarding regional character, both the NHANES and NHIS revealed the west to be higher in dietary supplementary usage than the other three regions of the country2,4,13 as did a study specific to seven western states.3 Our report of high usage in a western state confirms that pattern.

This study unlike other studies did not show significant correlation between usage and BMI, or education level, but gender effect was observed. Women took more supplements than men in this study, as many other studies have found.2,4,5,11,13,15,19,21,22 Not surprisingly, more men than women took lycopene and saw palmetto, which are associated with prostate health and sexual function, respectively. Also, more women than men took calcium, probably for prevention of osteoporosis, which has a higher incidence in women although both sexes are at risk. In this group of elders, usage declined with age. This does not conflict with other studies that find usage higher in older adults, in that this study looks at patterns within that age continuum and reveals a peak in the 71-to-75-year-olds. These findings parallel the NHIS results.5

One possible reason for the decline in supplement usage after age 75 may be financial. Although an analysis of socio-economic status was not performed, it may be that the expense of dietary supplements disproportionately affects individuals living on fixed incomes which tend to shrink with advancing age; and the usage rate might plateau and not decline across the oldest old if some dietary supplements were covered by federal or private health insurance. Another possible explanation is if the 75-year-olds carry the pattern into the ninth and tenth decades as they age, then the pattern historically began with their group for some reason unknowable at this time.

Although other studies3,4,11,13 report that non-Hispanic whites take more supplements than the other groups, this study does not. The Asian-Americans and the very few African-Americans whose data we have were part of the self-selecting pre-screened study set of the yoga/exercise group and both show higher usage than non-Hispanic whites. Study pre-selection was a possible cause of this high use. However, the DPS study was also a trial of complementary and alternative medicine (ie, the use of a botanical) and that group demonstrated the least usage of the three groups. One possible reason is that a behavioral lifestyle intervention draws volunteers with greater interest in complementary and alternative medicine than does a single substance, double blind placebo study whether nutriceutical or pharmaceutical.

Another aspect to consider regarding the high usage in non-white participants of this study compared to other studies, is that 89% of the Asian-Americans were specifically, Nikkei (Japanese-Americans) and this group’s economic status is said to approach that of non-Hispanic whites while the economic status of other Asian-American groups may not. Historically, the Japanese were among the first Asian immigrants and the native born second-generation is English-speaking, which was a criterion of the yoga/exercise study so that English-based neuropsychological tests could be performed. They were also highly educated, and old enough to be in the aging study. Generally speaking, the large category “Asian-American” may be too amorphous to be useful because it melds immigrant groups that are historically, culturally, socio-economically and geographically very distinct from one another. It is however, more defining than when not used at all as in the case of the NHANES or NHIS analyses and may partially account for the higher usages in the western region, which also has the highest concentration of Asian-Americans.

This study does show, as other studies have, that multivitamins were the most frequently taken dietary supplement and calcium and vitamins E and C were also in common use.3,4,13,22–24 Supplements unmentioned in previous studies of the elderly that show up in this “top 20” were glucosamine and chondroitin, GBE, fish oils and coenzymeQ10. Given current research including multi-center trials on such supplements, this demonstrates that some of the public, notably the younger elders, were already taking these readily available, relatively unregulated substances before conventional evidence for efficacy exists.

Unexpected results show that the oldest-old in a non-metropolitan rural setting were taking more supplements than those who live in the more metropolitan urban area, which is contrary to a previous report11 of urban and rural elders. In this study, a partial explanation comes from the screening of the metropolitan DPS group which did exclude 21 possible enrollees because they did not want to give up GBE, however even with all these rolled into the total of users, the percentage would rise to 62.6% which was still lower than the non-metropolitan KEAP group.

Also confirming the generally higher usage in the KEAP group, is the high use of folate and a multivitamin of anti-oxidants marketed for eye-health. Folate is associated with lowered levels of homocysteine and a consequent lowered risk for neurodegenerative disease as well as coronary heart disease. The multivitamin for vision was actively recommended by one of the community’s ophthalmologists. This kind of medical information, on both hyperhomocysteinemia25 and the role of oxidative-injury in aging,26 arises from theory and research of the past ten to fifteen years. The data on these two supplements show that in the particular case of Klamath County oldest old residents and their health care professionals, the access to and application of current thought and research may be as fast if not faster than in metropolitan areas such as Portland, Oregon.

This report adds to the evolving picture of dietary supplement usage by older adults. Although our database includes study participants it is still comparable to other surveys of dietary supplement use. The element of self-selection in volunteering for a study also holds true for surveys conducted by mail in that factors such as gender, independent living, and higher interest in health issues affect who is likely to respond.21

Dietary supplement use appears to be increasing in general, perhaps especially in Oregon, which has a high profile of alternative medicine institutions and practitioners. Portland is not only the site of the state’s only medical school but also of the Oriental College of Medicine, Western States Chiropractic College, and National College of Naturopathic Medicine. Furthermore, in Klamath County, Klamath Lake is a site for the nutriceutical industry product Aphanizomenon flos-aquae, a naturally growing blue-green algae that is considered to be higher in micronutrients than spirulina which is farmed. The Pacific-rim milieu of high awareness and practice of alternative medicine forms may distinguish the Oregon population from the rest of the United States. Also, this region has a high presence of Asian-Americans, which influences this report and may further distinguish it from previous studies.

We believe that high usage of supplements is concomitant with high interest in preventative and alternative medicine health lifestyle. Those who may be interested in studies of currently popular health forms like the yoga study27,28 are likely seeking out other alternative health practices such as acupuncture, naturopathy or use of dietary supplements, even more so than those enrolled in a single botanical study as in the use of GBE in dementia prevention. Supplement usage is but one indicator of a preventative and alternative health lifestyle and may affect outcome measures in interventional studies in much the same way that a generally healthier lifestyle confounded epidemiological studies seeking a link between dietary supplement usage and disease incidence and morbidity. For this discussion, see Ishihara J, et al, Enstrom J, et al, Clarke R, et al, and Eisenberg D, et al.18,22,24,29

The implications of high dietary supplement usage are widespread: (1) conventional clinical drug trials should now take into account any dietary supplement that may possibly confound drug effects; (2) experimental design in complementary and alternative medicine studies must now allow for and carefully pre-assess the way the potential participant is already engaged alternative health forms; and (3) since elders are the highest users of dietary supplements, the clinician will not only want to stay abreast of supplements of special interest to elders, but also, as in the case of GBE and warfarin, be aware of any botanical usage that may compound effects of a prescribed drug. Because this information may not be volunteered,30 it is up to the conventional medicine clinician to make an informed, non-judgmental query about all dietary supplement usage and other complementary and alternative health practices of their older patients.

Acknowledgments

Grants and Financial Support: National Institutes of Health (P50 AT0066, P30 AG08017); Northwest Health Foundation: Merle West Center for Medical Research. Klamath Falls, Oregon; and Oregon Small Grants program of the Alzheimer’s Association: Oregon-Idaho Chapter, 2001.

References

  • 1.US Food and Drug Administration, Nutrition Center for Food Safety and Applied Nutrition, Dietary Supplement Health and Education Act of 1994, Available at: http://vm.cfsan.fda.gov/~dms/dietsupp.html 1994. Accessed March 2005.
  • 2.Block G, Cox C, Madans J, et al. Vitamin supplement use, by demographic characteristics. Am J Epidemiol. 1988;127(2):297–309. doi: 10.1093/oxfordjournals.aje.a114805. [DOI] [PubMed] [Google Scholar]
  • 3.Medeiros D, Bock M, Raab C. et al. Vitamin and mineral supplementation practices of adults in seven western states. J Am Diet Assoc. 1989;89:383–386. [PubMed] [Google Scholar]
  • 4.Subar A, Block G. Use of vitamin and mineral supplements: Demographics and amounts of nutrients consumed. Am J Epidemiol. 1990;132(6) doi: 10.1093/oxfordjournals.aje.a115752. [DOI] [PubMed] [Google Scholar]
  • 5.Slesinksi M, Subar A, Kahle L. Trends in use of vitamin and mineral supplements in the United States: the 1987 and 1992 National Health Interview Surveys. J Am Diet Assoc. 1995;96(8):921. doi: 10.1016/s0002-8223(95)00255-3. [DOI] [PubMed] [Google Scholar]
  • 6.Lead Statement. Paper presented at: Dietary Supplement Usage in the Elderly, 2003; Bethesda MD.
  • 7.Decenniel Census, 2000: US Census Bureau; Available at: http://factfinder.census.gov/servlet/QTTable?ds_name=DEC_2000_SFl_U&geo_id=01000US&qr_name=DEC_2000_SF1_U_DP1 Accessed March 2005.
  • 8.Decenniel Census, 1990: US Census Bureau. Available at: http://factfinder.census.gov/servlet/QTTable?_ts=8506091761 Accessed March 2005.
  • 9.Census 2000, Oregon: Portland State University Population Center. Available at: hltp://www.upa.pdx.edu/CPRC/publications/2000census/index.html Accessed March 2005.
  • 10.SPSS v. 10.0. SPSS Inc. Headquarters, Chicago, IL 60606.
  • 11.Gray S, Hanlon J, Fillenbaum G, et al. Predictors of nutritional supplement use by the elderly. Pharmacotherapy. 1996;16(4):715–720. [PubMed] [Google Scholar]
  • 12.McIntosh W, Kubena K, Walker J, et al. The relationship between beliefs about nutrition and dietary practices of the elderly. J Am Diet Assoc. 1990;90:671–676. [PubMed] [Google Scholar]
  • 13.NHANESIII. Use of dietary supplements in the United States, 1988–94. vital and Health Statistics, from the Centers fur Disease Control and Prevention/National Center for Health Statistics, US Department of Health acid Human Services. 1999;Series II, No. 244.
  • 14.Norris J, Harnack L, Carmichael S, et al. US trends in nutrient intake: the 1987 and 1992 National Health Interview Surveys. Am J Public Health. 1997;87(No 5):740–746. doi: 10.2105/ajph.87.5.740. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Lyle B, Mares-Perlman J, Klein B, et al. Supplement users differ from nonusers in demographic, lifestyle, dietary and health characteristics. J Nutr. 1998;128:2355–2362. doi: 10.1093/jn/128.12.2355. [DOI] [PubMed] [Google Scholar]
  • 16.Sahyoun N, Jacques P, Russell R. Carotenoids, vitamins C and E, and mortality in an elderly population. Am J Epidemiol. 1996;144(No 5):501–511. doi: 10.1093/oxfordjournals.aje.a008957. [DOI] [PubMed] [Google Scholar]
  • 17.Bates C, Prentice P, Pols Jvd, et al. Estimation of the use of dietary supplements in the national diet and nutrition survey: People aged 65 years and over. An observed paradox and a recommendation. Eur J Clin Nutr. 1998;52:917–923. doi: 10.1038/sj.ejcn.1600665. [DOI] [PubMed] [Google Scholar]
  • 18.Ishihara J, Sobue T, Yamamoto S, et al. Demographics, lifestyles, health characteristics and dietary intake among dietary supplement users in Japan. Int J Epidemiol. 2003;32:546–553. doi: 10.1093/ije/dyg091. [DOI] [PubMed] [Google Scholar]
  • 19.Dorant E, Brandt PV, Hamstra A, et al. The use of vitamins, minerals and other dietary supplements in The Netherlands, Internal. J Vit Nutr Res. 1992;63:4–10. [PubMed] [Google Scholar]
  • 20.NHANES. Dietary Supplement Questionaire documentation: dsqdot.pdf. Available at: http://vww.cdc.gov/nchs/about/major/nhanes/NHANES99_00.htm 1999–2000.
  • 21.Brussard J, Brants H, Bowman M, et al. The study populalion: general characteristics and potential confounding factors. Europ J of Clin Nutr. 1997;51:S19–S24. [PubMed] [Google Scholar]
  • 22.Slesinski M, Subar A, Kahle L. Dietarj intake of fat, fiber and other nutrients is related to the use of vitamin and mineral supplements in the United States: The 1992 National Health Interview Survey. J Nutr. 1996;126(12):300l–3008. doi: 10.1093/jn/126.12.3001. [DOI] [PubMed] [Google Scholar]
  • 23.Enstrom J, Kanim L, Klein M. Vitamin C intake and mortality among a sample of the United States populalion. Epidemiology. 1992;3(3):194–202. doi: 10.1097/00001648-199205000-00003. [DOI] [PubMed] [Google Scholar]
  • 24.Kirk S, Cade J, Barrett J, et al. Diet and lifestyle characteristics associated with dietary supplement Use in women. Public Health Nutr. 1999;1(1):69–73. doi: 10.1017/s1368980099000099. [DOI] [PubMed] [Google Scholar]
  • 25.Clarke R, Smith DA, Jobst KA, et al. Folate, vitamin B12, and serum total homocysteine levels in confirmed Aizheimer’s disease. Arch Neurol. 1998;55(11):1449–1455. doi: 10.1001/archneur.55.11.1449. [DOI] [PubMed] [Google Scholar]
  • 26.Ames BN, Shigenaga MK, Hagen TM. Oxidants, antioxidants, and the degenerative diseases of aging. Proc Natl Acad Sci. 1993;90:7915–7922. doi: 10.1073/pnas.90.17.7915. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Stein J. Just Say Om. Time Magazine: August 4, 2003.
  • 28.Corliss R. The Power of Yoga. Time Magazine: April 15, 2001. [PubMed]
  • 29.Hoggatt K. Commentary: Vitamin supplement use and confounding by lifestyle. Int J Epidemiol. 2003;32:553–555. doi: 10.1093/ije/dyg222. [DOI] [PubMed] [Google Scholar]
  • 30.Eisenberg D, Kessler R, Rompay MV, et al. Perceptions about complementary therapies relative to conventional therapies among adults who use both: results from a national survey. Ann Intern Med. 2001;135:344–351. doi: 10.7326/0003-4819-135-5-200109040-00011. [DOI] [PubMed] [Google Scholar]

RESOURCES