The Multivitamin Debate
Marina MacDonald, MS, PhD,
4 years ago
17 min read
What does science say about multivitamin and mineral supplementation?
Dietary supplement use is common in the United States, with more than half of the population using such products.[1],[2],[3],[4] Similarly, a majority of health professionals, including physicians and dieticians, use dietary supplements themselves and recommend them to patients.[5],[6],[7] Among supplement users, multivitamin and mineral supplements (MVMs) are the most commonly used type (71%) of dietary supplement.[3]
Despite these trends, headlines seem to appear regularly over the question of whether taking MVMs will promote better health, with some articles purporting that supplements are a waste of money. Policy makers and many health professionals are often reluctant to recommend routine use of dietary supplements, in part because they are concerned that people will view the supplements as a substitute for a healthy diet, or that they will consume too much of a particular nutrient.
In this article, I get to the bottom of these controversies and present an array of data to help answer the question: are MVM supplements beneficial?
Clinical trials must consider nutrient status
The skeptics of dietary supplements often cite “null” studies that failed to show an effect of supplementation on a desired health outcome. In many cases, such studies also failed to assess the nutritional status of subjects at the beginning of the study. As Dr. Robert Heaney (Creighton University) notes, “Literally hundreds of studies of nutrient effects have reported null, or even adverse outcomes of nutrient interventions, almost always without reference to the basal status that prevailed in the study sample.”[8] In other words, vitamin or mineral supplements may not be effective in these trials because nutrient intakes among the participants are already at adequate levels.[8],[9],[10]
The National Institute of Health (NIH) Women’s Health Initiative (WHI) is an example of such a “null” study. Researchers, who were interested in studying the effects of calcium and vitamin D on the risk of bone fractures, randomly assigned women over the age of 50 to receive 1000 mg of calcium and 400 IU of vitamin D3 daily, or a placebo, for an average of seven years.[11] They reported that “supplementation resulted in a small but significant improvement in hip bone density, but did not significantly reduce hip fracture.” While this study is still widely cited, there’s more to the story than meets the eye.
Digging into the WHI study, the authors disclose that the participants were allowed to continue personal supplementation with calcium and vitamin D throughout the study, whether they were in the placebo or the intervention group. In fact, the average calcium intake of participants at baseline exceeded 1000 mg per day, close to the recommended dietary allowance (RDA) of 1200 mg for women age 50 and up. It’s no wonder, then, that additional calcium and vitamin D had no significant effect.
When a subsequent analysis was confined to women who were not already taking calcium and vitamin D, quite a different conclusion was reached: daily supplementation reduced the risk of hip fracture by 40% after five years.[12] Therefore, “Long-term use of calcium and vitamin D appears to confer a reduction that may be substantial in the risk of hip fracture among postmenopausal women.”
Considering eight different randomized controlled trials,[13] the National Osteoporosis Foundation (NOF) stated that “Calcium and vitamin D supplements are highly cost effective, and expanded use could considerably reduce fractures and related costs.”[14] The NOF also notes that “It is very difficult to get all the vitamin D you need from food alone. Most people must take vitamin D supplements to get enough to support bone health.”[15]
“It is very difficult to get all the vitamin D you need from food alone. Most people must take vitamin D supplements to get enough to support bone health.”
B-vitamin levels, aging, and cognition
B vitamins (folate, vitamin B12, and vitamin B6) are important for the metabolism of homocysteine (Hcy), an amino acid derived from methionine. If folate and other B vitamins are inadequate, Hcy accumulates in the blood. This condition (known as hyperhomocysteinemia, or HHcy) is associated with an increased risk for many age-related diseases, including cognitive decline and dementia,[16],[17],[18] which we all want to avoid! Thus there is great interest in determining whether B-vitamin supplementation helps lower Hcy and preserve cognitive function with age.
Folate deficiency is the most common cause of HHcy. The benefits of folate supplementation were clearly shown in a clinical study of men and women aged 50 to 70 years (with known HHcy) who were not already taking B-vitamin-containing supplements.[19] Subjects with low serum vitamin B12 levels were excluded in order to focus on folate in this study. Individuals who met these criteria were randomized to receive folic acid (800 mg per day), or a placebo, for three years. Serum folate concentrations increased fivefold, and plasma Hcy levels decreased by 26%, in the supplemented group.
The outcomes of this study were striking. Compared with placebo, the group supplemented with folic acid had slower rates of decline in memory and cognitive function as measured by standardized tests.[19] Remarkably, the memory performance of individuals who consumed the folic acid supplements was equivalent, on average, to that of someone who was 4.7 years younger! The researchers concluded that “Folic acid supplementation for 3 years significantly improved domains of cognitive function that tend to decline with age.”
Remarkably, the memory performance of individuals who consumed the folic acid supplements was equivalent, on average, to that of someone who was 4.7 years younger !
Although folic acid improved memory in this study, the results did not imply that folate supplementation could reduce the risk of Alzheimer’s disease. But in studies of individuals over the age of 70 with HHcy who already had mild cognitive impairment, daily high-dose B-vitamin supplementation (800 mg folic acid, 500 mg vitamin B12, 20 mg vitamin B6) not only improved cognitive function, but also slowed the atrophy of specific brain regions that are a key component of the Alzheimer’s disease process.[20],[21],[22]
Even with a balanced diet, it may be difficult to meet the RDA for folate (400 mg per day).[23] The regular use of MVMs containing 400 mg folic acid, along with vitamins B6, B12, and other micronutrients, has been shown to help maintain normal Hcy levels in healthy adults.[24],[25],[26] In fact, a recently-published study showed that folate and vitamin B12 supplementation in older adults was associated with a higher ratio of blood methionine to homocysteine, which in turn correlated with a reduced risk of brain atrophy and dementia.[27]
Are you really getting enough nutrients from your diet?
The U.S. Dietary Guidelines recommend that individuals obtain essential nutrients by consuming a balanced and varied diet including plenty of fruits, vegetables, whole grains, and low-fat dairy products.[28] In actuality, many of us do not achieve this goal on a daily basis. Let’s face it: the demands of modern life, including work, travel, stress, and family responsibilities, often make it difficult to achieve an optimal diet every day.
Nationwide surveys show that, although U.S. diets have improved slightly over the last decade,[29],[30] fewer than one in 10 Americans meet the recommendations for fruit and vegetable consumption,[31] and nutritional gaps are common.[32] The U.S. Dietary Guidelines Advisory Committee specifically identified vitamins A, C, D, and E, calcium, magnesium, iron, potassium, and choline as “underconsumed nutrients” in the U.S. population.[33]
Diets that eliminate or restrict entire food groups pose risks for micronutrient insufficiencies. Gluten-free diets, which eliminate wheat, rye, and barley, often have inadequate levels of vitamins B1, B12, and D, folate, calcium, iron, magnesium, and/or zinc.[34],[35],[36] The Paleolithic (“Paleo”) diet, which eliminates dairy, grains, and legumes, may provide insufficient levels of B vitamins, calcium, iodine, and magnesium.[37],[38] Vegetarians, and especially vegans who eliminate dairy, eggs, and meat products, may have inadequate intakes of vitamins B12 and D, calcium, choline, iodine, iron, and zinc.[39],[40],[41],[42],[43] Due to low calcium and vitamin D intake, vegans have an increased risk of osteoporosis and fractures,[44] and may benefit from supplementation. Scientists also advise that vegans, and anyone who significantly limits their intake of animal-based foods, should consider vitamin B12 supplementation.[45]
Inadequate micronutrient levels have been observed for popular weight loss diets,[46],[47] including the Atkins, Ornish, South Beach, and DASH diets.[48],[49] Ketogenic (Keto) diets provide inadequate levels of the majority of essential micronutrients.[50] MVMs can help adults satisfy their micronutrient needs in conjunction with various food patterns and diet plans.[50],[51],[52],[53]
Pregnancy poses additional nutrient demands to support the health of the mother and fetus. Approximately 30% of pregnant women do not take MVMs or folate-containing supplements, and may suffer from micronutrient insufficiencies.[54],[55],[56] Insufficient folate during pregnancy increases the risk of neural tube defects (NTDs) such as spina bifida,[57],[58],[59],[60] and the intake of sufficient folic acid reduces the incidence of NTDs by 50 to 70% if taken before conception and during the first trimester of pregnancy.[61] Thus the U.S. Preventive Services Task Force recommends that all women who are planning or capable of pregnancy take a daily supplement containing 400 to 800 mcg of folic acid.[62] A review of this recommendation notes that “habitual use of folic acid supplements is a more reliable method of ensuring adequate levels than diet.”[60]
Adults who did not consume MVM supplements were found to have a 40% risk of any nutrient inadequacy, compared to only 14% of those who used full-spectrum MVMs.
Across the population, the use of MVMs has been shown to reduce the risk of insufficiency for most vitamins and minerals.[63],[64],[65],[66],[67] Adults who did not consume MVM supplements were found to have a 40% risk of any nutrient inadequacy, compared to only 14% of those who used full-spectrum MVMs.[33]
Is MVM supplementation safe?
A panel of 14 international experts in nutritional science and health care recently concluded that “Use of MVMs is one approach to ensure that adequate micronutrient needs are met in support of biological functions necessary to maintain health. Long-term use of MVMs, not exceeding the upper limit of recommended intakes, has been determined to be safe in healthy adults.”[67]
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