Multivitamins can be marketed in the form of tablets, capsules, effervescent tablets, powders, liquids, gels or injectable formulations. With the exception of the latter category, which is available only under medical supervision and prescription, the rest of the multivitamins belong to the category of dietary supplements.
Most of the scientific evidence in this regard indicates that multivitamins do not prevent cancer, heart disease or other ailments in healthy people; therefore, there is no reason to recommend indiscriminate food supplementation. However, some population groups with specific nutritional needs can benefit from the intake of these products (for example the elderly, those at risk of macular degeneration, those who do not follow a balanced diet, etc.), while others can also take them simply as a precaution. (as in the case of folic acid for pregnant women or vitamin D for women entering menopause).
In Italy there is no real standardized scientific definition for multivitamins. In the United States, on the other hand, by multivitamin we mean:
"a supplement containing three or more vitamins and minerals, free from herbs, hormones or drugs, in which each vitamin and mineral is included at a lower dose than the tolerable upper intake level - determined by the" Food and Drug Board "- and free of health risks ".
Read also: Vitamin Supplements : vitamin C (ascorbic acid), vit B1 (thiamine), vit B2 (riboflavin), vit PP or B3 (niacin), vit B5 (pantothenic acid), vit B6 (pyridoxine), vit B7 (inositol), vit B8 or vit H (biotin), folic acid or folate, vit B12 (cobalamin)Multivitamins are available in a wide variety of formulas, sometimes based on age, gender or (as in prenatal supplements) highly specific nutritional needs. For example, a multivitamin for males might include less iron than that for fertile women, while a multivitamin for seniors might include more vitamin D and calcium than one for middle-aged adults. High-potency formulas provide at least 2/3 of the recommended dietary limit.
Rarely some nutrients such as calcium and magnesium are added at 100% of the recommended dose, as the amount of the single dose would become excessive. Most multivitamins come in capsule form, but tablets, powders, liquids and gels are also popular; injectable formulations are rarer.
, alcoholics, digestive and nutritional absorption complications, liver diseases, etc.In general, the medical advice on the use of multivitamins is to avoid them if not necessary. In particular, it is recommended to moderate the intake of vitamin A during pregnancy, due to the possible teratogenic effects that could determine a possible excess. On the other hand, the National Health Service (NHS) recommends 10 μg of vitamin D per day during pregnancy and breastfeeding, as well as 400 μg of folic acid for the first trimester (first 12 weeks of pregnancy). Some pregnant women may need to take iron and vitamin C supplements to counteract the anemia that often occurs during gestation, but only on the advice of a doctor. If pregnant, vegan women should seriously consider the need to supplement. l "feeding with cobalamin (vitamin B12). Sometimes, during gestation and breastfeeding it may be necessary to increase the calcium intake.
In the 1999-2000 National Health and Nutrition Examination Survey conducted in the US, 52% of adults reported taking at least one dietary supplement in the last month, and 35% confirmed regular use of multivitamins-multiminerals. From the results, women versus men, adults versus youth, whites versus Hispanics and blacks, and those with higher education versus those who studied less, were more likely to take multivitamins. use of multivitamins generally follow healthier and more nutritious diets. In addition, adults with a history of prostate and breast cancer have shown a greater aptitude for using multivitamins.
should take between 60 and 90 mg of vitamin C (ascorbic acid) per day (day). This range forms the center of the bell curve. The upper limit is instead of 2000 mg / day for adults, considered potentially dangerous.Pregnant women should consult their doctor before taking any multivitamins: as anticipated, an excess of vitamin A can cause disastrous effects on the unborn child (teratogenic).
In people who smoke (especially more than 20 cigarettes a day), former smokers, people exposed to asbestos and alcoholics, the long-term use of supplements of beta-carotene (provitamin A), retinol (vitamin A) and tocopherols ( vitamin E) can shorten life expectancy and increase the risk of lung cancer. In the United States, many famous brand multivitamins contain higher levels of certain vitamins and minerals than DRI / RDA amounts.
Severe vitamin and mineral deficiencies require medical treatment and can be very difficult to treat with over-the-counter multivitamins. In such situations, special vitamin or mineral forms with much higher potencies are available, both as individual components and as specialized formulations.
The intake of large quantities of multivitamins can cause a non-negligible risk of acute overdose, due to the toxicity of some components such as, for example, iron. However, unlike iron tablets, which can also be lethal for children , manifestations of toxicity from overdose of multivitamins are very rare.To reduce the risk in the event of gestation, rather strict limits have been imposed on the retinol content, and not surprisingly, special prenatal multivitamins have been designed for pregnancy.
As noted in the 2008 Harvard School of Public Health dietary guidelines, multivitamins should not replace a "healthy diet or compensate for" a frankly unhealthy diet. In 2015, the US Preventive Services Task Force analyzed studies that included data for approximately 450,000 people; the analysis found no strong evidence that multivitamins prevent cancer and heart disease, helping people live longer or "making them healthier in any way."
Scientific research on multivitamins
Provided certain precautions are taken, such as diet correction, taking multivitamins is generally considered safe, but further investigation is needed.
Evidence for the health effects of multivitamins comes largely from prospective cohort studies evaluating health differences between groups that take multivitamins and groups that do not. The correlations between intake and health are not highly specific, but may reflect the typical characteristics of the average multivitamin consumer. For example, it has been speculated that multivitamin users may, overall, suffer from more diseases than others. On the other hand, it has also been suggested that such users may, on the whole, have a greater focus on their own health. Both of these cases would make multivitamin supplements more useful in prospective cohort studies.
Cohort studies on multivitamins
In February 2009, a study of 161,808 postmenopausal women from the Women's Health Initiative clinical trials concluded after eight years of follow-up that "multivitamin use has little or no influence on risk." common cancers, cardiovascular diseases or total mortality ".
Another 2010 study published in the Journal of Clinical Oncology suggested that using a multivitamin during chemotherapy for stage III colon cancer had no effect on treatment outcomes.
A very large prospective cohort study published in 2011, involving over 180,000 participants, found no significant association between multivitamin use and all-cause mortality. There was also no impact of multivitamin use. on the risk of cardiovascular disease or cancer.
One cohort study that has received "extensive media attention is the PHS-II (Physicians" Health Study II). Performed double-blind on 14,641 US male physicians aged 50 and over (mean age of 64.3 years), from 1997 to June 1, 2011, with a mean analysis time of 11 years, this study compared the total incidence of cancer (excluding non-melanoma skin cancer) of participants taking a daily multivitamin (Centrum Silver, from Pfizer) or a placebo. Compared to placebo, men taking a multivitamin daily had a small reduction of the total incidence of cancer. No statistically significant effects were found for specific cancers or mortality. However, as pointed out in an editorial in the same issue of the "Journal of the American Medical Association," the researchers observed no difference in the effect of whether or not the study participants were rigorous in taking the multivitamin, reducing the dose-response relationship.
Using the same study, the researchers concluded that taking a multivitamin daily had no effect in reducing heart attack and other major cardiovascular events, myocardial infarction mortality, stroke and CVD.
Systematic reviews and meta-analyzes on multivitamins
One major meta-analysis, published in 2011, concluded that multivitamin use is not significantly associated with breast cancer risk. A Swedish cohort study indicated a similar effect, but overall this association was not statistically found. A 2012 meta-analysis of ten randomized, placebo-controlled trials, published in the Journal of Alzheimer's Disease, found that daily intake of a multivitamin may improve immediate recall memory, but does not affect in no other way the cognitive function.
Another "meta-analysis, published in 2013, found that multivitamin-multimineral treatment" has no effect on mortality risk, and a 2013 systematic review found that multivitamin supplement does not increase mortality and could, indeed, decrease it slightly. A 2014 meta-analysis reported that there is "sufficient evidence to support the role of multivitamin / mineral dietary supplements in reducing" age-related "cataract risk. A 2015 meta-analysis argued that the positive result on the effect of vitamins, referring to cancer incidence, found in the "Physicians" Health Study II "(above) should not be overlooked despite the neutral results of many other studies.
Looking at 2012 data, a study published in 2018 presented a meta-analysis on cardiovascular disease outcomes and all-cause mortality. It found that "no conclusive evidence has been demonstrated for the benefit of any supplement in all dietary settings (including vitamin deficiency and sufficiency), so any benefits should be related to possible risks." The study ruled out the benefits of taking regular supplements of vitamins C and D, beta-carotene, calcium and selenium. The reported results on taking niacin could indicate potentially harmful effects.
Expert opinion on multivitamins
A 2006 report from the "US Agency for Healthcare Research and Quality" concluded that "regular supplementation with a single nutrient or a mixture of nutrients for years has no significant benefits in primary prevention of cancer, cardiovascular disease, cataracts." , age-related macular degeneration or cognitive decline. ”However, the report noted that:
- multivitamins have beneficial effects for some subpopulations, such as those with poor nutritional status
- Vitamin D and calcium can help prevent fractures in older people
- zinc and antioxidants can help prevent age-related macular degeneration in high-risk individuals.
According to the Harvard School of Public Health: "... many people don't eat a healthy diet, that's why a multivitamin can help fill in certain gaps and can have health benefits." The U.S. Office of Dietary Supplements, a branch of the National Institutes of Health, suggests that multivitamin supplements may be useful for some people with specific health problems (eg, macular degeneration). However, it was concluded that "most research shows that healthy people who take a multivitamin are not less likely to get cancer, heart disease or diabetes." Based on current research, it is not possible to recommend or advise against the "use of multivitamins to live longer and healthier".
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