"These products provide a subtle, incremental effect. You can't use a sports supplement for a week and expect to gain pounds of muscle, but if used properly, research shows they can provide a slight, not overwhelming, edge," says Andrew Shoa, PhD, vice president for regulatory affairs for the Council for Responsible Nutrition, a trade association for the dietary supplement industry.
A 2013 study on herbal supplements found that many products were of low quality, one third did not contain the active ingredient(s) claimed, and one third contained unlisted substances. In a genetic analysis of herbal supplements, 78% of samples contained animal DNA that was not identified as an ingredient on the product labels. In some botanical products, undeclared ingredients were used to increase the bulk of the product and reduce its cost of manufacturing, while potentially violating certain religious and/or cultural limitations on consuming animal ingredients, such as cow, buffalo or deer. In 2015, the New York Attorney General identified four major retailers with dietary supplement products that contained fraudulent and potentially dangerous ingredients, requiring the companies to remove the products from retail stores.
Women who have very low levels of sunlight exposure or have naturally very dark skin are at risk of vitamin D deficiency. Those affected may include women who cover most of their body when outdoors, shift workers, those who are unable to regularly get out of their house or women in residential care. Women who have certain medical conditions or are on some medications may also be affected.
Herbal supplements are added to the diet for both nutritional and medicinal purposes. Herbs have been used for centuries in many traditional medicine systems, and as sources of phytochemicals, or substances found in plants that have notable effects in the body. Chinese medicine and Ayurvedic medicine from India, two of the world's oldest healing systems, use hundreds of herbal medications. Naturopathy and homeopathy, two other systems of natural healing, also rely on herbal preparations as their main sources of medication. The medicinal effects of herbs are getting scientific validation; about one-fourth of all pharmaceuticals have been derived directly from plant sources, including aspirin (found in willow bark), codeine (from poppy seeds), paclitaxel (Taxol), a patented drug for ovarian and breast cancer (from the Pacific Yew tree), and many others.
Nutritional density varies considerably geographically between different regions, even with the same agricultural methods. This was documented in the United States in 1948 by a researcher at Rutgers University in the so-called Firman Bear report.  At that time agriculture was little mechanized, and artificial fertilizers and pesticides were hardly used. The analysis found large differences in the content of minerals in the same food. The largest variations were found for potassium, sodium, boron and iron in spinach, while the greatest differences in calcium, magnesium and copper content were found in tomatoes.
The dietary supplements industry in the United Kingdom (UK), one of the 28 countries in the bloc, strongly opposed the Directive. In addition, a large number of consumers throughout Europe, including over one million in the UK, and various doctors and scientists, had signed petitions by 2005 against what are viewed by the petitioners as unjustified restrictions of consumer choice. In 2004, along with two British trade associations, the Alliance for Natural Health (ANH) had a legal challenge to the Food Supplements Directive referred to the European Court of Justice by the High Court in London.
Phytochemicals are compounds found in plants that may benefit human health. For example, carotenoids found in red, orange, yellow, and green plants (cooked tomatoes, carrots, squash, and broccoli) may inhibit cancer growth and cardiovascular disease, and boost the immune system. Flavonoids found in berries, apples, citrus, onions, soybeans, and coffee may fight inflammation and tumor growth. One can get a wide variety of phytochemicals by simply eating a varied diet that includes five to nine servings of fresh fruits and vegetables each day. (Locked) More »
It is possible to ingest too much of certain vitamins and minerals (vitamin A, calcium, iron, copper, selenium) which may exacerbate an existing imbalance or lack of another mineral (magnesium, zinc). It is also important to balance intake of fatty acids in the omega-6 and omega-3 series, as most people get too much omega-6 and not enough omega-3. Small children can be overdosed with adult doses of for example vitamin A or iron, and pills may be dangerous for babies or young children because they can get stuck in the throat. Therefore, I recommend consulting a doctor or nutritionist educated in orthomolecular medicine. Most people are likely to benefit from taking a broad-spectrum multivitamin/mineral supplement as a basic insurance against deficiencies.
FDA regulations for nutritional supplements differ in important ways from those for prescription or over-the-counter drugs. For one thing, pharmaceutical companies have to gather data showing that a new drug is safe and effective in order to get the FDA's approval to market the drug. Makers of dietary supplements don't have to show that sort of proof. Be sure to let your doctor know about any nutritional supplement you plan on taking so you can discuss whether it's right for you and the appropriate dose.
After basic nutritional requirements are supported, supplements may be used to target specific needs and health conditions. For instance, athletes, men, women, children, the elderly, and vegetarians have differing needs for nutrients, and an informed use of supplements would take these differences into account. People suffering from health conditions and diseases may use specific supplements to target their condition and to support the body's healing capacity by providing optimal amounts of nutrients.
Vitamin A can become toxic when taken in large amounts (over 100,000 International Units) on a daily basis over time, as can vitamin D. Substituting beta-carotene for vitamin A can alleviate this risk. Very large doses of minerals taken over long periods may have toxic effects in the body. Dosages far exceeding RDA's of vitamins are not recommended, nor are large doses of other supplements.
For example, while increased consumption of fruits and vegetables are related to decreases in mortality, cardiovascular diseases and cancers, supplementation with key factors found in fruits and vegetable, like antioxidants, vitamins, or minerals, do not help and some have been found to be harmful in some cases. In general as of 2016, robust clinical data is lacking, that shows that any kind of dietary supplementation does more good than harm for people who are healthy and eating a reasonable diet but there is clear data showing that dietary pattern and lifestyle choices are associated with health outcomes.