An estimated one-third of American adults and a quarter of children and teens take multivitamins, with U.S. sales totaling $8 billion in 2020, according to the National Institutes of Health’s Office of Dietary Supplements.
Some experts believe that a nutritious and balanced diet should be enough for many people. “I emphasize whole foods,” says Donald D. Hensrud, associate professor of nutrition and preventive medicine at Mayo Clinic College of Medicine. “I focus on helping my patients to have a healthy diet.”
But other experts say it’s more complicated because people often need more vitamins at certain stages of life or have health conditions that make it difficult to absorb vitamins from food. Some also need supplements in addition to multivitamins.
“Some nutrients are very difficult to get from food, like vitamin D, because very little occurs naturally in food,” says Bonnie Liebman, director of nutrition at the Center for Science in the Public Interest (CSPI). “Many older people don’t produce enough stomach acid to extract natural vitamin B-12 from milk, meat or eggs. Vitamin B-12 deficiency can cause irreversible nerve damage and can mimic dementia – something you want to avoid.
Scientists studying multivitamins say there is growing evidence that multivitamins may also provide additional health benefits, including delaying cognitive decline in older adults. A recent three-year study of more than 2,200 participants aged 65 and over funded by the National Institute on Aging, for example, found that those who take a daily multivitamin demonstrated significant cognitive improvement in abilities that tend to decline with normal aging, including short-term memory and executive functions such as decision-making, compared to those who received a placebo.
The unpublished results, which were presented at a scientific meeting in the fall, showed that multivitamin users demonstrated only 1.2 years of mental decline, instead of three years. In other words, they retained 1.8 years – almost 60% – of their mental acuity. The research was part of a larger trial that looked at the effects of multivitamins on cancer. The cognition results are expected to be published soon.
The larger study, known as COcoa Supplement and Multivitamin Results Studyor COSMOS, started in 2014 in an attempt to replicate the results of an earlier trial, the Physician Health Study II, which ran from 1997 to 2011. PHS II saw an 8% reduction in total cancers in people aged 50 and over who took daily multivitamins, but – unlike COSMOS – showed no cognitive advantage. The COSMOS study, on the other hand, which lasted only 3 and a half years, did not find a drop in cancers.
But the researchers – the same in both studies – point out that differences in the design and duration of the two studies explain the seemingly contradictory results.
“COSMOS just hasn’t been around long enough to unravel the effects of cancer,” says Howard Sesso, an associate professor of medicine at Harvard Medical School and one of the researchers. “For cancer, it really takes longer to detect the impact of nutritional interventions. We track participants, sending out surveys to see if they’re still taking multivitamins and to see if they’ve developed cancer.
There were also significant differences between the two studies in how they measured cognition. For example, the first baseline cognitive assessment in PHS II took place one to two years after participants started taking the pills, which means researchers would have missed any cognitive improvements that occurred during those first two years. , explains Sesso.
“COSMOS had a better study design,” he says. “The first baseline cognitive assessment took place before they started taking the multivitamin or the placebo. Potential benefits were seen in the one-, two-, and three-year follow-up assessments.”
Either way, experts say multivitamins are important for those who suffer from absorption disorders, the result of medications, gastric bypass surgery or digestive disorders such as Crohn’s disease, ulcerative colitis , inflammatory bowel disease and celiac disease.
Multivitamins can also provide the nutrients needed for specific life stages. Anyone planning to get pregnant should take multivitamins before and during pregnancy to ensure they get enough folic acid, which prevents fetal neural tube defects such as spina bifida. In contrast, postmenopausal women should avoid multivitamins that contain iron because they no longer lose iron during menstruation.
Some people also need additional supplements such as B-12 and vitamin D. The latter, necessary for bone health, is often insufficient in those who avoid sun exposure – a wise practice to prevent skin cancer. – and in those confined indoors, such as nursing. home residents.
Manson directed various studies on vitamin D supplements which suggest that taking extra vitamin D may reduce the risk of developing autoimmune diseases and reduce cancer deaths, but not prevent it. “Vitamin D can alter the biology of tumors so that they are less likely to metastasize,” she says.
She is also studying the effect of vitamin D on coronavirus symptoms – in particular, whether it can reduce upper respiratory tract infections – but there are no results yet. Still, she thinks taking a bit more is a good idea. (The recommended daily allowance or RDI is 600 international units, or IU, or 15 micrograms, but the amount varies between multivitamins.)
“During the pandemic, I recommend 1,000-2,000 IU, although the jury is still out in terms of benefits during covid,” she says. “It’s very safe. For bone health and other chronic conditions, 600-800 is enough.
Experts say it’s also smart to take vitamin B-12 supplements later in life. Most multivitamins contain 2.4 micrograms, the RDA for adults, but some people may need more, experts say.
“About 15% of people over the age of 65 have an early stage vitamin B12 deficiency,” says Hensrud. He suggests his patients in this age group take 500 to 1000 micrograms daily. “Vitamin B-12 is not well absorbed and has a high safety threshold,” meaning high doses won’t hurt, he says. “It’s probably the safest vitamin there is.”
The CSPI warns consumers not to rely on multivitamins to get enough calcium and potassium. “You’re better off getting enough potassium by filling half your plate with fruits and vegetables, rather than looking for a supplement,” Liebman says. “The need for a calcium supplement depends on how much food you eat.”
Premenopausal women and men through age 70 need 1,000 milligrams of calcium daily, she says. “You can’t rely on a multi to get it because it wouldn’t fit in a single tablet, and because you might get tired of food.”
Women need 2,600 milligrams of potassium per day, while men need 3,400 milligrams, she says. “Potassium can help lower blood pressure or keep it from rising with age,” Liebman says. In addition to fruits and vegetables, other sources of potassium include dairy products, beans and seafood.
Most experts agree that taking a multivitamin can’t hurt and could probably help, and people don’t need to spend a lot of money on it.
“I think a regular multivitamin and mineral supplement is reasonable for a lot of people,” Liebman says. “You don’t need the Cadillac of multivitamins. A Chevy is fine. Many store brands are usually perfectly adequate.
What vitamins should be in your multivitamin
Vitamin A 700-1050 mcg (2300-3500 IU)
Vitamin D 20-25 mcg (800-1000 IU)
Vitamin E 13-35 mg (20-80 IU)
Thiamine (B-1) 1.1mg or more
Riboflavin (B-2) 1.1mg or more
folate Premenopausal women 660-680 mcg DFE (dietary folate equivalent) (400 mcg folic acid); all others 400-680 mcg DFE (235-400 mcg folic acid)
Vitamin B-12 2.4 mcg or more
Calcium Don’t rely on a multivitamin
The iron Premenopausal women 18 mg; all others (no more than 8 mg)
Potassium Don’t rely on a multivitamin
(Note: “or more” does not mean that a nutrient is safe at any dose, but that multivitamin levels are unlikely to be high enough to cause harm. This list does not apply to prenatal multivitamins for pregnant women. Consult your doctor. )