Millions of Americans take vitamins every day, yet headlines swing back and forth: one year vitamins are "a waste of money," the next a big study says a daily multivitamin may help your memory. So which is it? The honest answer is that it depends on which vitamin, who is taking it, and what you expect it to do. Here is a plain-language look at what the largest, best-designed studies have actually found.
The short answer
- Filling a real gap works. When someone is low in a nutrient, or has a higher need for it, supplementing it is well supported. Folic acid before pregnancy, vitamin B12 for many older adults are clear examples, as are the myriad of studies that show the benefits of proper vitamin D levels (which must be supplemented if not getting enough sunshine as food sources of vitamin D are extremely poor.
- A few findings are genuinely encouraging, especially recent research on multivitamins and memory in older adults, and vitamin D and autoimmune disease.
- Quality matters. The FDA does not approve supplements before they are sold, so where you buy them and which brands you choose make a difference. Having someone on your side who is an expert on these molecules known as nutrients is crucial! That is why I am glad you are here! I aim to educate you on your best supplement choices, with over 25 years of clinical experience with hundreds of my clients. I see what works and what does not. I see what is a fair price, and what is a rip-off. I see what is bad quality and what you would want for any biohacking.
Multivitamins: modest but real signals
The Physicians' Health Study II followed nearly 15,000 male doctors over age 50 for more than ten years. Men who took a daily multivitamin had about an 8% lower rate of total cancer than men who took a placebo (JAMA, 2012). That is a small effect, and the study included only men, but it came from a long, well-controlled trial.
The more recent COSMOS trial enrolled more than 21,000 older adults. A daily multivitamin did not significantly change overall cancer or cardiovascular events over about three and a half years. Where COSMOS did find a benefit was the brain. Three separate COSMOS studies tested memory and thinking in older adults; when researchers pooled more than 5,000 participants, a daily multivitamin was linked to slower cognitive aging, by an estimated two years, compared with placebo (American Journal of Clinical Nutrition, 2024).
The U.S. Preventive Services Task Force reviewed this whole body of research in 2022 and concluded there is not enough evidence to recommend for or against multivitamins to prevent heart disease or cancer. In other words: not proven for those goals, but not shown to be harmful, and with some promising signals.
Vitamin D: not a cure-all, but more than "nothing"
The VITAL trial gave nearly 26,000 U.S. adults 2,000 IU of vitamin D3 a day or a placebo for about five years. There were fewer cancer deaths in the vitamin D group. (New England Journal of Medicine, 2018).
A follow-up analysis of the same trial found something unexpected: people taking vitamin D had a 22% lower rate of new autoimmune diseases such as rheumatoid arthritis, psoriasis and thyroid autoimmune disease (BMJ, 2022). That is one trial, and it needs to be repeated, but it is a meaningful finding from a large, randomized study.
Vitamin D needs vary a lot from person to person depending on sun exposure, skin tone, body weight and diet, and a simple blood test can lead your supplementation need.
Where the evidence is strongest: filling known gaps
Folic acid before and during early pregnancy. This is one of the best-proven uses of any supplement. The U.S. Preventive Services Task Force gives an "A" grade to a daily supplement with 400 to 800 micrograms of folic acid for anyone who is planning or could become pregnant, to help prevent neural tube defects in the baby.
Vitamin B12 for people who absorb it poorly or don't eat animal foods. According to the National Institutes of Health, B12 deficiency is common in older adults. When a person tests their B12 levels and they do eat animal products, I usually suspect an absorption issue as a molecule known as intrinsic factor is released by the parietal cells of the stomach for getting that B12 into the system. Others at higher risk include vegans and vegetarians, people taking metformin or acid-reducing medicines (such as omeprazole), and people who have had weight-loss or stomach surgery. For these groups, a supplement can make a huge difference.
The common thread that I see in clinical practice, looking at nutrient panels, genetics, and diet, is that a very good quality multi vitamin can fill in many gaps and give you peace of mind.
When more is not better
Some of the most important vitamin research showed harm from high doses of single nutrients:
- Beta-carotene in smokers. The CARET trial gave high-dose beta-carotene plus 25,000 iu of vitamin A to more than 18,000 heavy smokers and asbestos-exposed workers. It was stopped early in 1996 because lung cancer and deaths were higher in the supplement group. This study is well known, and we must note that this was from high doses. I only recommend a 25,000 iu does of vitamin A to my clients when they are dealing with infections. For someone to just start taking this high 25,000 iu amounts is a bit daft to do unless you are treating something. And if you are a smoker then this would not be part of an anti-infection protocol for you. capsule
- Vitamin E and prostate cancer. In the SELECT trial of more than 35,000 men, those taking 400 IU of a synthetic form of vitamin E, dl-alpha-tocopheryl acetate had a 17% higher rate of prostate cancer than men on placebo (JAMA, 2011). We must note that this is a synthetic form of vitamin E: the kind that you will find in the very cheapest of the cheap supplements, like the ones found in your grocery store with their own branding on it. Once again, you must know what molecules you are dealing with! I was at the local dollar store recently picking up some home things and a few gadgets, and to my amazement they had a supplement shelf, and you guessed it, bottles of vitamins and minerals for $1.50. Guess what I saw? Dl-alpha-tocopheryl acetate labeled as vitamin E! There are many forms of vitamin E on the market and some are absolutely astounding in what they can offer for health. Vitamin E is not just one molecule. There are well over 10 molecules that can all be labeled as vitamin E so you just have to know what you are dealing with and that is why I am here to help.
Based on findings like these, the U.S. Preventive Services Task Force specifically recommends against taking beta-carotene or vitamin E to prevent heart disease or cancer. This is a big reason to choose doses thoughtfully and to get guidance rather than stacking high-potency single nutrients on your own.
Why quality and sourcing matter
Unlike prescription drugs, supplements are not reviewed by the FDA before they reach store shelves. In the FDA's own words, it "is not authorized to approve dietary supplements for safety and effectiveness before they are marketed." That puts the responsibility on manufacturers and on you as the buyer.
A few practical steps help:
- Choose established professional brands that publish their testing standards and use third-party testing.
- Buy from authorized sources. Many professional brands advise against buying their products on Amazon or eBay because of counterfeit, expired or improperly stored products.
- Check doses against what you actually need, and watch for overlap if you take several products.
- Talk with a knowledgeable health professional or pharmacist, especially if you take prescription medicines, since some supplements interact with them.
The bottom line
Vitamins are not magic, and they are not worthless. The research supports using them strategically: to fill real gaps, to meet higher needs at certain life stages, and in a few areas, like memory in older adults, where recent trials look promising. Choosing well-made products at sensible doses matters as much as choosing the right nutrient.
If you would like access to professional-grade brands such as Thorne, Pure Encapsulations, Designs for Health and Integrative Therapeutics, you can set up a free account through my Fullscript store and save 20% on your first order and 10% on every order after that. If you have questions about what makes sense for you, email me at DrPaulGannon@gmail.com.
Sources
- U.S. Preventive Services Task Force: Vitamin and Mineral Supplementation to Prevent CVD and Cancer (2022)
- Physicians' Health Study II: multivitamins and cancer in men (JAMA, 2012)
- COSMOS trial findings
- Mass General Brigham: Multivitamins improve memory and slow cognitive aging (2024)
- National Cancer Institute: VITAL trial results on vitamin D and cancer (2018)
- Harvard Gazette: Vitamin D reduced rate of autoimmune diseases by 22% (BMJ, 2022)
- USPSTF: Folic Acid Supplementation to Prevent Neural Tube Defects
- NIH Office of Dietary Supplements: Vitamin B12 fact sheet
- Fred Hutch: About the CARET trial
- National Cancer Institute: SELECT trial results
- FDA: Information for Consumers on Using Dietary Supplements
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before starting any supplement, especially if you are pregnant, nursing, or taking medication.