Although as a general rule, dietary supplement labeling and marketing are not allowed to make disease prevention or treatment claims, the U.S. FDA has for some foods and dietary supplements reviewed the science, concluded that there is significant scientific agreement, and published specifically worded allowed health claims. An initial ruling allowing a health claim for calcium dietary supplements and osteoporosis was later amended to include calcium supplements with or without vitamin D, effective January 1, 2010. Examples of allowed wording are shown below. In order to qualify for the calcium health claim, a dietary supplement much contain at least 20% of the Reference Dietary Intake, which for calcium means at least 260 mg/serving.
Poor nutrition may be one of the easiest conditions to self-diagnose. Look at the food pyramid and the suggested servings. Look at your diet. Are you getting the recommended daily amounts of fruits and vegetables? Enough calcium? Read the labels and compare what you eat to what you need. You may discover that even if your weight is ideal, you are not getting enough nutrition.
Salt, caffeine and alcohol intake may interfere with the balance of calcium in the body by affecting the absorption of calcium and increasing the amount lost in the urine. Moderate alcohol intake (one to two standard drinks per day) and moderate tea, coffee and caffeine-containing drinks (no more than six cups per day) are recommended. Avoid adding salt at the table and in cooking
Folate or vitamin B9 (also known as folic acid when used in fortified foods or taken as a supplement) is another nutrient that many women don’t get enough of in their diets. Folate can greatly reduce the chance of neurological birth defects when taken before conception and during the first few weeks of pregnancy. Folate can also lower a woman’s risk for heart disease and certain types of cancer, so even if you’re not planning on getting pregnant (and many pregnancies are unplanned), it’s an essential nutrient for every woman of childbearing age. In later life, folate can help your body manufacture estrogen during menopause.
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.
As with all dietary supplements, in the United States inappropriate label health claims such as preventing or treating disease are opposed by the FDA and deceptive advertisements by the Federal Trade Commission. Probiotic foods and dietary supplements are allowed to make claims using Structure:Function vocabulary as long as human trial evidence is adequate. In 2005, the FDA issued a Warning Letter to UAS Laboratories for disease treatment claims (colds, flu, ulcers, elevated blood cholesterol, colon cancer...). The company revised label and website content and continued to sell the product. In 2011 the company was found to have resumed the label and website claims, and the FDA seized product and stopped production. In 2010 a FTC action was brought against a probiotic food company for exaggerated health claims, resulting in a multimillion-dollar fine and revisions to future advertising. In the European Union a more restrictive approach has been taken by the EFSA. All proposed health claims were rejected on the grounds that the science was not sufficient, and no health claims are permitted. Foods with live microorganisms (yogurt, kefir) can be sold, but without claims.
One exception, he says, is seniors, who may need additional B-12 because as we get older, we absorb less of it. Most of us should skip the supplements and get our Bs from grains, dark green vegetables, orange juice, and enriched foods. People with certain medical conditions or who take drugs that interfere with vitamin absorption may also require supplementation.
When it comes to omega-3 fatty acids (omega = ω) such as EPA and DHA, children may be given cod liver oil and served fish and/or other seafood 2-3 times a week. It is important to check the dose of vitamin A supplied, as it can be toxic in high doses, especially for children. One problem with cod liver oil today is that vitamin D has been removed during processing, thus changing the natural ratio of the two vitamins so that we ingest relatively too much of vitamin A. 
Without the energy you get from things like carbohydrates, your blood sugar levels will likely dip which may lead you to feel sluggish and fatigued. And if you let yourself get to hungry, Rachele Pojednic, Ph.D., assistant professor in the nutrition department at Simmons College and professor at the Harvard Extension School, tells SELF that appetite-inducing hormones like ghrelin may even cause you to become shaky or sweaty.
Vitamins can be natural or synthetic. Natural vitamins are extracted from food sources, while synthetic vitamins are formulated in laboratory processes. The only vitamin for which there is a noted difference between the natural and synthetic forms is vitamin E. The natural form is labeled d-alpha-tocopherol while the synthetic form is named dl-alpha-tocopherol, with the extra "l" signifying laboratory production. Natural vitamin E has been shown to be slightly more absorbable by the body than the synthetic version, although for other vitamins no significant differences in absorption have been noted.
"Staying well-hydrated helps your body function properly, and it also helps make sure you don’t overeat," Pam Bede, M.S., R.D. with Abbott’s EAS Sports Nutrition, tells SELF. But it's not just that staying hydrated keeps you from overeating. According to Maxine Yeung, M.S., R.D., owner of The Wellness Whisk, sometimes you may feel hungry when, in fact, you're actually thirsty. Basically, no harm can come from drinking a glass of water.
Vitamin C protects the brain and nervous system from damage caused by stress because the synthesis and maintenance of chemical neurotransmitters such as adrenaline and noradrenaline requires adequate levels of vitamin C.  Vitamin C is also needed to repair collagen which is essential for skin, blood vessels, bones and joints, and muscles. When these are damaged by physical stress, extra vitamin C is necessary. A controlled trial of 91 adults who experienced increased anxiety and stress 2-3 months after an earthquake in New Zealand in 2011 was divided into three groups, two were given a broad spectrum supplement of micronutrients in low or higher doses.  The supplements were found to alleviate the experience of stress, with the biggest dose having the biggest effect.
Part of the reason why so many women fail to get the amount of iron they need is because one of the best sources of iron is red meat (especially liver) which also contains high levels of saturated fat. While leafy green vegetables and beans are also good sources of iron—and don’t contain high levels saturated fat—the iron from plant foods is different to the iron from animal sources, and not absorbed as well by the body. Other foods rich in iron include poultry, seafood, dried fruit such as raisins and apricots, and iron-fortified cereals, breads, and pastas.