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Do Multivitamins do more Harm than Good?

Author: Jonathan Zhao ‘27

Editor: Yilin Xie ‘26

For millions of Americans, vitamin and mineral supplements have become part of the daily routine. According to a 2019 poll, more than 4 out of 5 Americans take vitamin or mineral supplements [1]. Yet, only a quarter of those taking vitamin or mineral supplements have been diagnosed with a nutritional deficiency [1]. The health effects of these nutritional supplements for those not diagnosed with a deficiency are unclear and controversial. Some studies have shown not only are there no overall benefits to taking multivitamin/mineral supplements, but that they can also increase the risk of certain cancers and other non-communicable diseases [2]. Moreover, this emphasis on supplements can overshadow the importance of a healthy diet to good overall health.

In 2022, the annual sales of these supplements surpassed 50 billion dollars. Why are they so popular in the United States [3]? The popularity of vitamins took hold when diseases caused by nutritional deficiencies such as pellagra, rickets, and scurvy were common, and many eminent scientists advocated for the use of vitamins before the 1990s. In fact, the word vitamin is derived from the words “vital” and “amine” because vitamins are required for life and must be obtained from the diet. For example, Linus Pauling, a two-time Nobel Laureate, believed that vitamin supplements, especially vitamin C, can prevent cancer and increase the life expectancy of cancer patients [2]. Randomized studies sponsored by the National Cancer Institute and Mayo Clinic later debunked this belief, although such beliefs still prevail to this day [4].  Even people who are skeptical about multivitamins often still believe that even if they do not help, they do not harm. Thus, multivitamins have become a part of the lifestyles of many who want to improve their health through the convenient consumption of a pill or gummy every day yet do not want to avoid tasty, unhealthy food [2]. This highlights the common misconception that people can get away with not eating a nutritional diet with a multivitamin. Of course, the multivitamin industry which makes billions of dollars each year also plays a role. They often use commercials to spread inaccurate or misleading information, manipulating the results of scientific studies. Moreover, unlike the case in many other countries, the US FDA does not require manufacturers to conduct human research to prove that the vitamins are safe or effective [2]. 

In the US, the use of supplements contributes substantially to the total vitamin and mineral intake in the population. US adults derive at least five times more vitamin B6, thiamin, and riboflavin and 15 to 20 times more vitamin B12 and E from supplements than from foods [5]. Although this is beneficial to an extent, there has been an increase in the prevalence of people consuming vitamins and minerals above the upper level of tolerability. This is especially true due to food fortification and enrichment — such as the addition of B vitamins to flour and vitamin D to milk — which have reduced the need for further supplementation [5]. As a result, the National Health and Nutrition Examination Survey found excess intake of nutrients such as niacin, zinc, calcium, and folate among US adults. However, there is a lack of high-quality studies on whether the long-term overconsumption of several nutrients may pose a health concern [6]. 

One of the first studies that showed that vitamins may be detrimental to health was conducted in 1994 on middle-aged male smokers in Finland. In this demographic, it showed that vitamin A and E supplements increased the risk of lung cancer by 18% and mortality (mainly from lung cancer and cardiovascular disease) by 8% [7].  In 2009, a famous study known as the Selenium and Vitamin E Cancer Prevention Trial (SELECT Trial) yielded a conclusion that was contrary to the belief that selenium and vitamin E supplementation were cancer fighters. Instead, the supplements increased the risk of prostate cancer among healthy men [8]. As a result, the World Cancer Research Fund and the American Institute for Cancer Research have advised against the use of dietary supplements for cancer prevention among the general public [9]. Moreover, certain vitamins and minerals are also linked to risks to cardiovascular health. A study by the Women’s Health Initiative found that calcium supplements, whether taken alone or in combination with vitamin D, were associated with an increased risk of cardiovascular events, notably myocardial infarction [10].

However, it is important to note that these studies were very large and randomized to reflect the general population. In some cases, vitamin and mineral supplements are effective for certain subgroups that are not reflected in the studies. For instance, iron supplements during pregnancy are proven to significantly lower the risk of anemia and perinatal complications. Physician-recommended treatment for disorders such as osteoporosis, as well as other diseases, may necessitate the use of multivitamin/mineral supplements (MVMs) or individual vitamins or minerals [2].

Overall, vitamin and mineral supplements do not provide overall health benefits for those without a deficiency and may increase health risks in the long term. Studies have shown that nutrient intake from foods, not supplements, reduces overall mortality due to interactions among various nutrients and other bioactive substances present in foods [6]. Thus, emphasizing a healthy diet, rather than the consumption of supplements, remains crucial to promoting overall health and well-being.


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