The goal of this paper was to examine factors associated with regular MVU among a multi-ethnic sample of low-income housing residents representing a range of ages. Little research to date has investigated factors associated with MVU among lower-income or racially/ethnic diverse populations. In light of the potential benefits of multivitamins, particularly for groups at higher risk for nutritional deficiencies, and ongoing epidemiological evaluations of the protective effects of multivitamins and specific nutrients (e.g. Vitamin D and calcium) for chronic diseases, research is warranted to understand patterns of use among this population.
Sociodemographic factors found to be significantly associated with MVU were generally consistent with prior findings in the literature among the U.S. population.15,16,21–28
Specifically, females, older residents, and those who identified as White/Other had higher rates of rates of regular MVU than their referents. While there were borderline significant findings for poverty level, with residents living above poverty marginally more likely to take multivitamins, there were not any differences by education, employment, or insurance status. This is in contrast to prior research on indicators of socioeconomic position (SEP) and MVU. For example, among a national sample of U.S. adults, 21.4% of people with less than a high school education used multivitamin/multimineral supplements in the previous month compared to 43.9% of people with more than a high school education.15
Although we had some variability in education in our sample, our findings here may be explained by the fact that our sample is predominately very low income with little variability with respect to income.
It is interesting to note that Hispanics had the lowest rates of MVU compared to other racial/ethnic groups. Though research typically suggests that Whites are more likely to regularly use multivitamins than other racial/ethnic groups, most studies examining MVU to date have largely been conducted among predominately White samples, with a few exceptions.23,37
Recent data from the Multiethnic Cohort Study (1999–2001) found that regular multivitamin/mineral use (at least one a week over the past year) was reported by 50% participants, ranging from 38% among Native Hawaiians, 43% among African-Americans, 44% among Latinos, 52% among Japanese Americans, and 57% among Whites.37
Data from the National Health and Nutritional Examination Survey found multivitamin use in the past month to be nearly 40% among non-Hispanic Whites, compared to 23% and 20% respectively among non-Hispanic Blacks and Mexican-Americans.15
More research among diverse racial and ethnic samples is clearly needed.
With respect to health-related variables, we found a non-significant association between current health status and multivitamin use. There have been mixed findings with respect to health status, medical conditions, and multivitamin use in the literature. One study among a large cohort of men and women in western Washington from the VITAL study (ages 50–76) found that multivitamins were not more likely to be used by cancer survivors than cancer-free controls, with the exception of women with a history of breast cancer having somewhat higher use.30
Other research suggests that supplement and/or multivitamin users are more likely to have been diagnosed with a disease and be on a diet, but are also more likely to rate their health status as excellent or good.15,26,31
Since health behaviors and patterns have been found to cluster together,38,39
we hypothesized that residents with higher levels of physical activity and lower body mass indexes (BMIs) would be more likely to regularly use multivitamins than those who were less active and had higher BMIs. Interestingly, among this population, we did not find that MVU clustered with other health behaviors or patterns. However, it is important to note that this population tended to have low levels of MVU, low levels of PA, and high rates of obesity; therefore, the limited variability may in part explain these findings.
In examining health care provider/patient relationships, we hypothesized that residents who have a regular health care provider, have seen their health care provider recently (in the last 12 months), perceive that their health care provider knows them well, or leave all screening tests to their provider would be more likely to regularly use multivitamins than their counterparts. Though little research has specifically looked at these specific provider-related characteristics in relation to MVU, research suggests that health care providers may play an influential role in determining whether women of childbearing age take multivitamins.17,29,40,41
In contrast to what we hypothesized, this research suggested that there was no difference in MVU by any of the provider-related characteristics. Unfortunately, from this data, we are not able to determine if providers actually recommended taking multivitamins. However, we would speculate that in the context of strong provider/patient relationships, it is probably necessary for the provider to also specifically recommend MVU to ultimately increase intake among this population.
Importantly, while patterns of use are fairly consistent with the literature in terms of who is more likely to take multivitamins, the overall rates of MVU intake found in this study (26%) are much lower than reported in the general U.S. population. It is important to note that the overall evidence available related to the long-term protective effects of multi-vitamins is not conclusive with respect to cardiovascular disease and cancer. While prior observational studies have suggested possible protective benefits for some cancers,42,43
as well as cardiovascular disease, osteoporosis, and birth defects, 44,45
the evidence has been deemed insufficient by the US Clinical Preventive Services Task Force at this time. There are several large randomized clinical trials underway that may provide more definitive evidence in the future. In the meantime, it is critical for future studies to address this issue, particularly from the perspective of disparities. Multivitamins are a relatively simple and low cost ‘intervention’, and if they do have preventive effects and certain population groups are not utilizing them, it could explain persistent disparities at least to some extent.
Study limitations and strengths should be addressed. We achieved a response rate of 53% which ranged from a low of 34% to a high of 92% across the housing sites. Nevertheless, we targeted, recruited and enrolled 1554 participants, which represents a large, ethnically-diverse underserved population. Furthermore, the response rate reported here is consistent with other response rates that have been reported from community-based studies.46,47
However, the low response rates does introduce the possibility of bias in model estimates and associations. While we do not have any information on non-responders in this study, it is well-documented that people who do not respond to surveys have poorer health behaviors than those who do respond, suggesting that if there is any bias, it is likely that we are overestimating the prevalence of MVU. Multivitamin intake was collected by self-report, which may have biased our estimates. However, such biases, which would likely have been due to socially desirable reporting, if anything would have biased our results in terms of over-estimating MVU. Given that the overall use rates were so low (26%), this is unlikely. There may also have been confounding variables that we did not assess. This study has limited generalizability to other populations other than low-income, urban, racial/ethnic minorities living in public housing.
A number of strengths should also be noted. Little research to date has explored MVU among low income populations. The ODH sample is particularly interesting, because, despite its low income status, over 95% of participants had health insurance and most had an ongoing relationship with a health care provider. Thus, we are better able to isolate the role of provider-characteristics from access-related issues. This is also a relatively large and diverse sample, in terms of race/ethnicity, gender and age. Finally, this study had significant data related to other health behaviors and provider-patient relationship, which makes it possible to explore relationships not typically evaluated in the literature.
Findings from this study suggest that the prevalence of MVU is comparatively lower among lower-income, multi-ethnic housing residents than among national samples. This is troubling given that low-income populations likely have a higher prevalence of nutrient deficiencies and therefore may receive greater benefits from MVU. Furthermore, our findings indicate that sociodemographic factors primarily drive use among this population. These are valuable data for both the scientific and public health community. First, it could help explain some of the differences in disease prevalence and morbidity seen in low-income and racially/ethnically diverse populations. Furthermore, if clinical or public health recommendations are made that encourage MVU, this population will be made a priority for educational interventions. Thus, the results presented here provide a basis for later research to build upon in understanding factors associated with MVU among underserved populations. Our findings may also have important implications for research on other dietary supplements. For example, if research continues to suggest the roles of Vitamin D and calcium in preventing cancer,2–7
we may soon see recommendations for daily supplements of these vitamins. Thus, our findings are useful in helping us think about how to effectively meet those recommendations. Future research may want to further explore some of the psychosocial, attitudinal, and cultural factors that may mediate the association between sociodemographic factors and MVU.