Vitamin and mineral supplements have become a $32.7bn (£24.2bn) global industry, with over 74% of Americans and two-thirds of Britons admitting to regular use. While these products are marketed as an easy solution to nutritional gaps, research shows their benefits are far from guaranteed. Scientists, including JoAnn Manson from Harvard and Bess Dawson-Hughes from Tufts University, have conducted large-scale studies that question whether these pills truly improve health or, in some cases, may even cause harm.
Table of contents:
- Why Americans and Britons turn to supplements
- Controversy over high-dose supplementation
- The role of vitamin D in public health
- Multivitamins and their potential benefits
Why Americans and Britons turn to supplements
Vitamins and minerals are essential micronutrients that the body cannot produce. We obtain them primarily through diet. Key examples include vitamin A for vision and skin health, vitamin C for immune support, and vitamin K for blood clotting. Essential minerals such as calcium, magnesium, and potassium are also crucial in small amounts.
However, research highlights a shortfall in healthy eating habits:
- The average American consumes only 50% of the recommended daily intake of fruits and vegetables.
- Diets high in processed food have replaced fresh, nutrient-rich meals.
- Certain populations including the elderly and those with restricted diets face higher deficiency risks.
Bess Dawson-Hughes notes that insufficient produce intake likely results in missing essential nutrients. This gap has encouraged the growth of the multivitamin market, but the health benefits are still under debate.
Controversy over high-dose supplementation
The idea that mega-doses of vitamins could prevent disease gained popularity in the 1970s, largely due to Nobel laureate Linus Pauling’s claims about vitamin C. Modern research has debunked these claims and shown that excessive intake can be dangerous.
Notable risks include:
- Vitamin D overdose can lead to seizures, coma, and even death.
- Excess vitamin A may cause blurred vision, dizziness, and in extreme cases, death.
- High doses of vitamin E have been linked to a greater risk of haemorrhagic stroke due to its blood-thinning effect.
- Large beta-carotene doses may increase lung cancer risk in smokers and interfere with the absorption of other beneficial carotenoids.
Studies such as Manson’s double-blind trials show that antioxidants like vitamin C, beta-carotene, and vitamin E offer no protection against cancer or cardiovascular disease. In some cases, high intakes may become harmful by turning into pro-oxidants.
The role of vitamin D in public health
Vitamin D is essential for bone health and immune function. While the body can produce it from sunlight exposure, many regions lack sufficient year-round sunlight. UK guidelines recommend vitamin D supplementation for everyone between October and March. Similar advice applies to individuals living north of 37° latitude or south of 37° in the southern hemisphere.
The Vital trial, involving over 25,000 U.S. adults, found:
- No reduction in overall cardiovascular disease or cancer incidence.
- A 17% decrease in cancer mortality among vitamin D users.
- A 25% reduction in metastatic cancer deaths in those supplementing for over two years.
- A significant drop in autoimmune disease rates such as rheumatoid arthritis and psoriasis.
However, multiple trials including Vital, Vida, and D-Health found no benefit for bone fracture prevention, possibly because participants already had adequate vitamin D levels.
Multivitamins and their potential benefits
Evidence suggests that daily multivitamin use may benefit certain groups, especially older adults. Manson’s Physician’s Health Study II showed:
- An 8% lower cancer risk in long-term users.
- An 18% reduction in cancer incidence among participants over 70.
The Cosmos trial found a 60% slower rate of cognitive decline in multivitamin users over three years. Additional research links them to lower cataract risk.
Populations that may benefit include:
- Adults over 60, particularly those with limited diets.
- Pregnant women, who are advised to take folic acid to prevent neural tube defects.
- Vegetarians or those consuming little fish, who may need omega-3 supplements.
- Individuals with conditions like Crohn’s disease or ulcerative colitis, which impair nutrient absorption.
- Nursing home residents, who may require vitamin D and calcium to prevent osteoporosis.
A French study found that nursing home residents given vitamin D and calcium had a 40% lower risk of hip fractures.
Experts stress that more is not necessarily better. Both Manson and Dawson-Hughes emphasize that for most people, a balanced diet remains the most effective source of nutrients. Supplements may serve as an insurance policy for those with dietary gaps, but excessive intake can be harmful. As research continues, the focus remains on identifying which groups truly benefit from supplementation and ensuring they receive the right dosage without unnecessary risk.
Quelle: BBC