Should We All Take Vitamin Supplements? Who Really Needs Them

Vitamin supplements can help fill nutritional gaps in our diet, but they’re far from a perfect solution.

The global vitamin and mineral supplement market is worth an estimated $32.7bn (£24.2bn), with more than 74% of Americans and about two-thirds of Britons using them in hopes of improving their health. Yet, research on their benefits is mixed — some studies find no significant advantages, while others warn of potential harm. This raises important questions: Who should be taking supplements, and who actually needs them?

Why we take vitamins and minerals
Vitamins and minerals are essential nutrients our bodies can’t produce on their own, so we must get them from food. Examples include vitamin A for vision and skin health, vitamin C for immunity, vitamin K for blood clotting, and minerals like calcium, magnesium, and potassium. These are known as micronutrients because we need them in much smaller amounts than macronutrients like carbohydrates, proteins, and fats.

A healthy diet — rich in vegetables, fruits, grains, nuts, dairy, and fish — remains the best way to meet these needs. But with processed foods and fast meals becoming the norm, many people fall short. According to Bess Dawson-Hughes of Tufts University, the average American consumes only about half the recommended fruits and vegetables. This dietary gap has fueled interest in supplements.

The myth of “more is better”
The idea that high doses of vitamin C could cure the common cold became popular in the 1970s, championed by Nobel Prize-winning chemist Linus Pauling. But studies have since debunked it. Today, some supplements contain 500–1,000% of the daily recommended value, even though such products are loosely regulated, sometimes contain undeclared ingredients, and lack robust randomized controlled trial evidence.

Excessive intake, or “mega-dosing,” can be dangerous. Too much vitamin D may cause increased thirst, frequent urination, seizures, coma, or even death. Overdosing on vitamin A can trigger headaches, dizziness, muscle pain, and — in severe cases — coma or death.

What studies reveal
Early research on antioxidants like beta-carotene, vitamin C, and vitamin E found no protection against cancer or cardiovascular disease. In fact, large doses of beta-carotene have been linked to higher lung cancer risk in smokers, and high doses of vitamin E can raise the risk of bleeding strokes. Extremely high antioxidant levels can also become pro-oxidants, potentially damaging cells. Furthermore, excess amounts of one nutrient can hinder the absorption of others — for example, too much beta-carotene can reduce uptake of lutein from leafy greens.

Vitamin D: a special case
Vitamin D, vital for bone health, can be made by the body through sun exposure and also obtained from certain foods. In regions with limited winter sunlight, such as the UK or anywhere north of 37° latitude, supplementation is advised.

The large VITAL trial, involving over 25,000 U.S. adults, found no effect of vitamin D on preventing heart disease, stroke, or overall cancer incidence. However, it showed a 17% lower cancer death rate in the supplement group — rising to 25% among those who took it for two or more years. Vitamin D also reduced autoimmune diseases like rheumatoid arthritis.

Despite this, evidence on fracture prevention is mixed. Some studies found benefits in older adults with low vitamin D, but others, including the VITAL, VIDA, and D-Health trials, did not — likely because many participants already had sufficient vitamin D levels.

The case for multivitamins
Long-term research suggests daily multivitamins might help older adults. In the Physicians’ Health Study II, participants over 70 saw an 18% reduction in cancer risk after 11 years of supplementation. The 2023 COSMOS trial found that multivitamins slowed cognitive decline by 60% over three years and were linked to fewer cataracts. These effects may be due to poorer diets or nutrient absorption in older age.

Who might benefit from supplements
Experts generally agree that most people can meet their needs through diet, and whole foods also offer benefits like fibre. But supplements can help in specific cases:

• Adults over 60 may see reduced cancer risk and slower cognitive decline from daily multivitamins.

• Pregnant women should take folic acid to reduce birth defect risks.

• People who eat little or no fish may benefit from omega-3s.

• Those with absorption issues from conditions like Crohn’s disease, ulcerative colitis, or certain medications (e.g., metformin) may require supplementation.

• Elderly people, especially nursing home residents, may benefit from vitamin D and calcium to prevent fractures — with some studies showing up to 40% fewer hip fractures in this group.