A dietary supplement is a manufactured product intended to supplement the diet when taken by mouth as a pill, capsule, tablet, or liquid. A supplement can provide nutrients either extracted from food sources or synthetic, individually or in combination, in order to increase the quantity of their consumption. The class of nutrient compounds includes vitamins, minerals, fiber, fatty acids and amino acids. Dietary supplements can also contain substances that have not been confirmed as being essential to life, but are marketed as having a beneficial biological effect, such as plant pigments or polyphenols. Animals can also be a source of supplement ingredients, as for example collagen from chickens or fish. These are also sold individually and in combination, and may be combined with nutrient ingredients. In the United States and Canada, dietary supplements are considered a subset of foods, and are regulated accordingly. The European Commission has also established harmonized rules to help insure that food supplements are safe and properly labeled. Among other countries, the definition of dietary supplements may vary as drugs or other classes of ingredients used in supplement products.
(OMNS Sept 12 2018) One of the most vitamin-restrictive countries in the world is Norway. There, authorities limit potencies to only slightly higher than RDA (Recommended Dietary Allowance) levels for dietary supplements sold outside of pharmacies. The traditional reasoning is that most people receive the nutrients they need from a "balanced diet."  The authorities are also obsessively concerned that some vitamins and minerals are harmful in high doses. And, since an intake of water-soluble vitamins in excess of needs is excreted in the urine, Norwegian "experts" advise that taking supplements is a waste of money. Accordingly, the argument goes, the public should be protected not only from possible harm, but also from wasting money on unnecessary nutrients. The official policies on nutritional supplements vary within OECD (Organization for Economic Cooperation and Development) countries. Some are more liberal, while others are even more restrictive.
USDA's food icon, MyPlate, serves as a quick visual reminder to all consumers to make healthy food choices when you choose your next meal, built off of the Dietary Guidelines for Americans. MyPlate can help prioritize food choices by reminding us to make half of our plate fruits and vegetables and shows us the other important food groups for a well-balanced meal: whole grains, lean proteins, and low fat dairy.
In 2015, the Australian Government's Department of Health published the results of a review of herbal supplements to determine if any were suitable for coverage by health insurance. Establishing guidelines to assess safety and efficacy of botanical supplement products, the European Medicines Agency provided criteria for evaluating and grading the quality of clinical research in preparing monographs about herbal supplements. In the United States, the National Center for Complementary and Integrative Health of the National Institutes of Health provides fact sheets evaluating the safety, potential effectiveness and side effects of many botanical products.
A well-known example is vitamin C, which can effectively fight viral infections, prevent or reverse disease caused by bacteria, and help the body detoxify organic and inorganic toxins.  Vitamin C also reduces the risk for cancer, strengthens connective tissues (collagen), and counteracts stress by increasing the adrenal´s production of cortisol. The dose required is set according to the body's need. Nobel Price Laureate Linus Pauling suggested that an optimal daily intake of vitamin C could vary from at least 250 mg up to 20 grams per day.  Because unabsorbed vitamin C attracts water into the gut, some people may experience loose stools, gas and/or diarrhea by ingesting only 1-2 grams at a time, while others with a higher level of stress may tolerate 5-6 grams or more. The dose that causes loose stools is called the "bowel tolerance" for vitamin C.  To avoid the laxative effect of high doses, it is best to take vitamin C throughout the day in smaller divided doses.
Some supplements that were found to have health benefits in observational studies turned out, with more rigorous testing, to be not only ineffective but also risky. Vitamin E, which was initially thought to protect the heart, was later discovered to increase the risk for bleeding strokes. Folic acid and other B vitamins were once believed to prevent heart disease and strokes—until later studies not only didn't confirm that benefit but actually raised concerns that high doses of these nutrients might increase cancer risk.
Sodium. Sodium is found in salt, but most of the sodium we eat does not come from salt that we add while cooking or at the table. Most of our sodium comes from breads and rolls, cold cuts, pizza, hot dogs, cheese, pasta dishes, and condiments (like ketchup and mustard). Limit your daily sodium to less than 2,300 milligrams (equal to a teaspoon), unless your doctor says something else. Check the Nutrition Facts label for sodium. Foods with 20% or more of the “Daily Value” of sodium are high in sodium.
Nutrition is particularly important when you are pregnant. Weight gain during pregnancy is normal—and it's not just because of the growing fetus; your body is storing fat for lactation. The National Academy of Sciences/Institute of Medicine (NAS/IOM) has determined that a gain of 25 to 35 pounds is desirable. However, underweight women should gain about 28 to 40 pounds, and overweight women should gain at least 15 pounds. The IOM has not given a recommendation for an upper limit for obese women, but some experts cap it as low as 13 pounds. If you fit into this category, discuss how much weight you should gain with your health care professional. Remember that pregnancy isn't the time to diet. Caloric restriction during pregnancy has been associated with reduced birth weight, which can be dangerous to the baby.
Many women and teenage girls don't get enough calcium. Calcium-rich foods are critical to healthy bones and can help you avoid osteoporosis, a bone-weakening disease. Additionally, recent studies suggest that consuming calcium-rich foods as part of a healthy diet may aid weight loss in obese women while minimizing bone turnover. The National Institute of Medicine recommends the following calcium intake, for different ages:
Not getting enough fiber can lead to constipation and can raise your risk for other health problems. Part of healthy eating is choosing fiber-rich foods, including beans, berries, and dark green leafy vegetables, every day. Fiber helps lower your risk for diseases that affect many women, such as heart disease, diabetes, irritable bowel syndrome, and colon cancer. Fiber also helps you feel full, so it can help you reach and maintain a healthy weight.
Research from Tufts University nutrition scientists shows that Americans are drinking so much soda and sweet drinks that they provide more daily calories than any other food. Obesity rates are higher for people consuming sweet drinks. Also watch for hidden sugar in the foods you eat. Sugar may appear as corn syrup, dextrose, fructose, fruit juice concentrate or malt syrup, among other forms, on package labels.
A year later, a second Harvard study added to the concern. The Physicians' Health Study of 20,885 men did not evaluate diet per se, but it did measure the blood levels of ALA in 120 men who developed prostate cancer and compared them with the levels in 120 men who remained free of the disease. Men with moderately high ALA blood levels were 3.4 times more likely to develop prostate cancer than men with the lowest levels; curiously, though, men with the very highest levels were only 2 times more likely to get the disease.
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 instance, foods rich in vitamin E and beta-carotene are healthy and can help reduce cancer risk. However, the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) recommend against taking vitamin E or beta-carotene for the prevention of cardiovascular disease. People who smoke or are at risk for lung cancer also should avoid beta-carotene. It can increase their risk of lung cancer.