Approximately one third of Americans take a daily multivitamin. Is this doing any good? Scientific studies tell us, probably not.
Given that there’s an established link between essential vitamin and mineral deficiencies and increased risk of chronic disease (see The Link Between Nutrients and Disease Risk), and that there are studies have confirmed lower prevalence of some nutrient deficiencies among middle aged and older adults who take a daily multivitamin, it would be reasonable to posit that taking a multivitamin would reduce risk of chronic disease. However, a vast collection of high-quality studies have failed to show any protective impact from taking a daily multivitamin.
Multivitamins Don’t Improve Health Outcomes
An important 2013 meta-analysis showed that multivitamins had absolutely no effect on all-cause mortality, a general marker of health and longevity, nor on mortality associated with cardiovascular disease. A 2018 meta-analysis showed that multivitamin and multimineral supplements provided absolutely no benefit to cardiovascular disease incidence or outcomes, including coronary heart disease and stroke. A 2013 systematic review showed no benefit of vitamin and mineral supplements in the prevention of cardiovascular disease or cancer. Large prospective studies have confirmed no protective effect of multivitamins against a wide variety of cancers in both men and women.
An important 2019 study helped to shed some light on this question by comparing the health impact of nutrients from foods versus supplements. This study revealed that consuming sufficient vitamin A, vitamin K, magnesium, zinc and copper from food—but not from supplements—reduced all-cause mortality and mortality associated with cardiovascular disease. Furthermore excess calcium from supplements—but not from food—increased risk of mortality from cancer. This study reinforces the importance of achieving nutrient sufficiency from food and even highlights some potential harmful effects from supplementation. Supplemental calcium is also associated with calcium oxalate kidney stones, and elevated serum levels of folic acid (a common form of vitamin B9 found in supplements) has been associated with increased cancer risk and can mask vitamin B12 deficiency.
Why Don’t Multivitamins Work?
Why don’t multivitamins improve health outcomes? One explanation could be that the vitamins and minerals in multivitamins are poorly absorbed. While we still need studies to measure the exact bioavailability of supplemental nutrients in a variety of conditions, there is reason to believe that we’re pooping out much, if not most, of a multivitamin’s nutrients, including examination of: the molecular forms used, competition with other nutrients in the formula, the binders used to create a tablet, digestive processes differences when taken with food or an empty stomach, and/or the contribution of the gut microbiome to nutrient absorption.
There is a large amount of interaction between nutrients in terms of absorption and utilization. For example,
- high levels of zinc decrease absorption of iron and copper;
- vitamin C improves absorption of iron;
- flavonoids increase absorption of vitamin C;
- vitamin D improves absorption of calcium, phosphorous and magnesium; and
- consuming fat concurrently with fat-soluble nutrients like vitamin K and carotenoids increases absorption.
While nutrient synergy is often inherent to foods—for example the flavonoids in oranges increase absorption of their vitamin C by up to 8 times—it’s unusual to see vitamin and mineral supplements take these impacts into account.
Furthermore, studies have shown that multivitamin tablets can take 4 to 6 hours to dissolve in environments designed to model the human gut, which is far too long—in order for the nutrients within a multivitamin to be efficiently absorbed, the tablet would need to dissolve fully within 20 to 30 minutes so that the vitamins and minerals within can be transported into the body within the small intestine.
Multivitamins Aren’t Enough
Another explanation for the apparent uselessness of multivitamins could be that vitamin and mineral supplements do not meet enough of the diet shortfalls to actually reduce chronic disease risk, i.e., you just can’t supplement your way out of a nutrient-poor diet, at least not with the supplements currently available. It’s possible that the amount of essential vitamins and minerals actually absorbed from a multivitamin still aren’t enough to meet the body’s needs in the context of both deficiency and inadequate intake from food. There is plenty of evidence that this is the case for vitamin D—while many multivitamins contain 400IU to 1,000IU, that amount is likely inadequate to address most vitamin D insufficiency (it’s typical for a doctor to recommend 2,000IU to 5,000IU of vitamin D3 daily if your levels are low).
In addition, multivitamin supplements generally focus on essential vitamins and minerals and do not contain prebiotics like fiber, important non-proteinogenic amino acids or peptides, omega-3 fatty acids, nor phytonutrients; and if they do, the quantity is almost always insufficient. So, even if the vitamin and mineral content of a multivitamin is sufficient to supplement the diet, important nutrients are still missing.
Analyses that account for regular food, fortified foods and supplements show that we still aren’t getting adequate amounts of essential nutrients. According to one analysis using data from the National Health and Nutritional Examination Survey (looking at food intakes and supplements for more than 16,000 Americans over the age of two) and the estimated average requirements (EAR values) for each nutrient:
- 70% of Americans still don’t consume enough vitamin D
- 60% of Americans still don’t consume enough vitamin E
- 45% of Americans still don’t consume enough magnesium
- 38% of Americans still don’t consume enough calcium
- 34% of Americans still don’t consume enough vitamin A
- 25% of Americans still don’t consume enough vitamin C
- 8% of Americans still don’t consume enough vitamin B6, vitamin B9, or zinc
- A smaller percentage (less than 6%) of Americans still don’t consume enough vitamin B1, vitamin B2, vitamin B3, vitamin B12, phosphorus, iron, copper, or selenium
Certainly, targeted supplementation recommended by a healthcare provider in response to laboratory test results indicating severe nutrient deficiency still has a role to play in the overall health equation. However, the concept of a multivitamin as nutritional insurance has been busted.
So, save your money or instead apply those savings to more whole and minimally-processed foods!
Expand to see all scientific references for this article.
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