By David Kiefer, MD, German H. Rodriguez, MD, and Zehra Siddiqui, DO
Dr. Rodriguez is a Third-Year Resident at the Beth Israel Medical Center/Institute for Family Health Residency in Urban Family Practice, New York. Dr. Siddiqui is an Integrative Medicine Fellow at the Institute for Family Health, New York.
Dr. Rodriguez and Dr. Siddiqui report no financial relationships relevant to this field of study.
In 2011, Americans spent more than $30 billion on dietary supplements.1 It has been estimated that 49% of the U.S. population, overall, uses some form of dietary supplement,2 whereas the National Health and Nutrition Survey (NHANES), a project of the U.S. Centers for Disease Control and Prevention (CDC), estimated that 70% of adults older than age 71 use some form of dietary supplement.3 The 2007-2010 NHANES data showed that multivitamins (MVIs) were the most commonly used dietary supplement in the United States.4
People take MVIs for a variety of reasons. Data from the 2007-2010 NHANES showed that most adults took MVIs to improve and maintain general health.4 People surveyed who were older than age 60 were more likely to take MVIs for site-specific reasons (i.e., bone, heart, and eye health). Another study showed that dietary supplement, and presumably MVI, users (vs nonusers) were more likely to have been diagnosed with a disease and to be on some kind of diet but to perceive their health status as being good.5 This was supported by other research showing that people take dietary supplements as nutrition insurance.6
Furthermore, dietary supplement use has consistently been associated with several demographic groups and behavioral characteristics: women, older age, higher education level, regular physical activity, and being non-Hispanic white,6 as depicted in Table 1. These are not necessarily the demographics typically associated as being the least healthy or unwell. It begs the question, then, whether MVIs should be routinely recommended and for whom. This review will summarize some recent MVI research results, focusing on older adults, to assist clinicians in making a decision about who most needs that category of dietary supplement.
Research Investigating Benefits of MVIs
At first glance, it might seem obvious that people in the United States need MVIs. Since the 1970s, there has been a steady decline in intake of fruits and vegetables, followed closely by an increase in intake of nutrient-poor, high carbohydrate foods.7 In 2005, the CDC estimated that only 32.6% of adults consumed fruit two or more times per day and only 27.2% ate vegetables three or more times per day.8 A low fruit and vegetable intake becomes increasingly more likely in the elderly due to poor appetite, eating disability, and underlying pathology.9 Even with an adequate intake of fruits and vegetables, it may be difficult to meet daily recommended intakes (DRI)due to changes in nutrient content of foods, which can depend on the food’s origin and subsequent processing. For example, some frozen vegetables may lose up to 95% of their folate content after being frozen for only 3 months.10 Another analysis found that the content of nutrients in dehydrated fruits and vegetables drastically decreased after a shelf life of 3 months.11
It could be postulated that addressing these vitamin deficiencies with the regular use of MVIs would translate into tangible health benefits. Researchers have attempted to study the effect of MVIs on various outcomes in older adults, most commonly cognition, cancer, and infections, and for psychological benefits. The results have been variable. For example, one systematic review did not show any benefit with MVI use to prevent or halt the progression of cognitive decline in healthy or cognitively impaired older adults.12 In contrast, 16 weeks of supplementation with a combined multivitamin, mineral, and herbal formula seemed to benefit memory in elderly women at risk of cognitive decline.13 In this latter study, of course, it is difficult to tease out the effect attributable to just the MVI component of the formula. Researchers have also tried to determine the cognitive effects of individual components of MVIs. One randomized, controlled trial, however, failed to show a statistically significant decrease in the risk of cognitive impairment and dementia with 24 months of vitamin B supplementation compared to placebo among cognitively intact older men aged 75 years and older.14 Another randomized, controlled trial of cognitively intact older adults with elevated homocysteine levels found supplementation with B vitamins for 2 years lowered homocysteine levels, but did not demonstrate any improvement in cognitive performance compared with placebo.15
The effect of MVI use on cancer is complicated, if not controversial. The oft-quoted Physicians’ Health Study II followed 14,641 male U.S. physicians ages 50 years and older (mean age 64.3 years; SD 9.2 years) who were taking a common multivitamin on a daily basis from 1997-2011. The investigators wanted to provide trial data to weigh in on the debate of whether adults who take dietary supplements for cancer prevention should be taking them at all. They found that daily MVI supplementation modestly but significantly reduced the risk of total cancer (hazard ratio [HR], 0.92; 95% confidence interval [CI], 0.86-0.998; P = 0.04). There was no significant effect on prostate cancer (HR, 0.98; 95% CI, 0.88-1.09; P = 0.76), colorectal cancer (HR, 0.89; 95% CI, 0.68-1.17; P = 0.39), or other site-specific cancers. There was no significant difference in the risk of cancer mortality (HR, 0.88; 95% CI, 0.77-1.01; P = 0.07). It is unclear if these results are actually due to the MVIs, or due to other factors, such as increased cancer screening.16
Another study found no convincing evidence that the use of MVIs or any specific vitamin affects the occurrence or severity of prostate cancer.17 The National Institutes of Health weighed in on this debate and concluded that there is insufficient evidence to recommend for or against the use of MVIs in cancer prevention.18
The General Population Nutrition Intervention Trial (NIT) assessed the impact of daily vitamin and mineral supplementation on the primary prevention of esophageal and gastric cancer. The trial involved 29,584 adults age 40-69 years without any history of cancer or debilitating disease in Linxian, China, from 1985-1991. During this 15-year period, villagers were visited on a monthly basis. The participants were given an antioxidant combination of selenium, vitamin E, and beta-carotene, which in the study was known as "factor D." The population of this region of China has some of the highest rates of esophageal and gastric cancer in the world. The authors proposed a link between previously reported dietary deficiencies in this province and the high incidence of esophageal and gastric cancer. They found that patients who received "factor D" had a lower overall mortality (HR, 0.95; 95% CI, 0.91; P = 0.09) and gastric cancer mortality (HR, 0.89; 95% CI, 0.79-1.00; P = 0.43). A follow-up study showed that these beneficial effects were still evident up to 10 years after the cessation of supplementation. These effects were mainly seen in participants younger than 55 years of age. It is not clear if the benefits of "factor D" are due to the combination or one of its components.19
With respect to infections, a randomized, controlled trial failed to show an effect of MVI supplementation on the incidence and severity of acute respiratory tract infection in 652 patients older than 60 years.20 Of note, the study participants were well-nourished and non-institutionalized, perhaps an issue when thinking about who might be most in need of, and benefit from, MVIs.
Psychological Benefits of MVI Use
Some psychological benefits are surfacing in the medical literature for people who take MVIs. For example, a double-blind, randomized trial compared patients taking MVIs with placebo, and found that the MVI group showed a greater increase in energy level and mental alertness (P = 0.022), as well as improvements in mood and emotional well being (P = 0.027). These beneficial effects on energy levels were most noticeable in female participants (P = 0.020). Also, 10% more participants in the MVI group reported better sleep than the placebo group, but this was not statistically significant (P = 0.87). No major adverse effects were reported.21
In addition, MVI use in men ages 50-69 years led to significant improvement in scores on a General Health Questionnaire (P = 0.016), but not in symptoms of depression (P = 0.241) nor anxiety (P = 0.188).22 Another study — this time in 225 hospitalized, acutely ill patients aged 65-92 years — found that MVIs improved depressive symptoms (P = 0.021).23 Some of these results connect with hypotheses that brain function may benefit from vitamin intake greater than the current DRI, especially in patients with subclinical nutritional deficiencies.24
Research Demonstrating Possible Risks Associated with MVI Use
One possible adverse effect associated with MVI use in older individuals is that MVIs may lead to supplement-supplement or supplement-pharmaceutical interactions. It is estimated that 25-50% of persons older than the age of 65 years were taking five or more medications, a threshold above which the risk of pharmaceutical-pharmaceutical interactions is significant.25 Add to this the fact that 6.9-26.2% of these older adults in the same study were taking more than one herbal medicine, nutraceutical, or vitamin — a situation now referred to as "polyherbacy" or dietary supplement polypharmacy.26,27 Even though MVIs may be seen as innocuous as an isolated treatment, in the context of numerous other ingested substances, interactions may occur.
When MVIs are part of a treatment regimen, patients — especially those with impaired cognition, visual acuity, or physical functioning — can become confused about their pharmaceutical dosing, leading to medication errors.25 Alternatively, patients with dementia may defer their health care decisions to their families who may opt to substitute certain medications in favor dietary supplements.26 Though these phenomena are not unique to MVIs, it is a reminder to clinicians to inquire about any dietary supplement use as well as to clarify pharmaceutical and supplement dosing and adherence. In addition, on this note, it is important to be aware of excess intake, especially when individual vitamins are being consumed in addition to MVIs.
MVI use, as with other dietary supplements, often takes place outside the purview of health care providers. This may actually occur in a majority of patients,4 although there is some debate in the medical literature about the actual percentage of nondisclosure. There are many reasons for this, a complete discussion of which is beyond the scope of this article. For example, in some cases, healthy people are taking MVIs to have a more active role in the maintenance of their general health.25 In other cases, patients might be responding to patient-directed advertising in magazines and other news media, again without adequate discussion with a medical provider;28 this use may not be in line with evidence-based indications.29
MVIs, one of the most commonly used dietary supplements, may have some utility for a variety of psychological conditions, as much as the evidence for cancer prevention, improvement in cognition, and infection prevention, are less than convincing. It is unclear what is the best dose of the individual components, or, related to that, which brand is the best. The mechanism for this effectiveness or ineffectiveness remains in the realm of hypothesis and theory, but it may be related to dietary changes, depauperate foods, and some cellular mechanisms that remain to be ferreted out. This review offers some thoughts from the medical literature about why MVI use may not be entirely without adverse effects.
At this point, based on the quality of the evidence available, it is difficult to definitively say that MVIs will prevent or treat any medical condition, as much as there are some hints to that effect in the medical literature. Even if it were possible to say that MVIs could improve symptoms or decrease risk of contracting a particular disease, the next issue, and a very important one, is which MVI would be the most effective? There are many varieties and dosages of MVIs; the state of the science is still in its infancy about this aspect of this commonly used supplement. Not to discount the conscious and subconscious benefit of having a "dietary insurance policy," this is where an individualized discussion with the patient may come into play. It is important to be aware of a person’s perception of dietary supplements, and, if relevant, encouraging his/her active participation in this goal for wellness. It goes without saying that MVIs should not take the place of adequate intake of a variety of fruits and vegetables. Along these lines, this counseling should take into account nutritional status, underlying pathologies (including impaired swallowing, cognition, other medical problems), risks of polyherbacy and supplement-pharmaceutical interactions, and finances (MVIs can be costly). An intelligent risk-benefit discussion between doctor and patient, individualized and seasoned with some of the scientific facts and unknowns, as with many other aspects of integrative medicine, seems to be the best course of action for MVI use in older individuals.