Scientific evidence shows that some dietary supplements are beneficial for overall health and for managing some health conditions. For example, calcium and vitamin D are important for keeping bones strong and reducing bone loss; folic acid decreases the risk of certain birth defects; and omega-3 fatty acids from fish oils might help some people with heart disease. Other supplements need more study to determine their value. The U.S. Food and Drug Administration (FDA) does not determine whether dietary supplements are effective before they are marketed.
Nutritional supplements are products to aid you when you are not getting enough nutrients from your meals. Most common supplements used by people today are multivitamins, protein shakes and meal replacement shakes. In todays times where people are so busy and just don't have the time to sit down to a meal supplements have become then next best thing. These days they have supplements for just about anything from fish oils, Vitamin B or fat burning. While most of these supplements will help you some of them are not good for you. So always consult your doctor first before taking any supplement.
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.
Health care experts haven't reached a consensus on the issue of vitamin and mineral supplements. Many say that if you are healthy and eat a well-balanced diet, you don't need any. But not all of us eat a well-balanced diet. And sometimes, you may follow a nutritious diet and still be deficient. Many women fail to get the adequate amount of vitamins and minerals. Stress increases your need for vitamins and minerals, especially C, B-complex and zinc.
Medicine companies follow FDA regulations. Some makers of dietary supplements follow the U.S. Pharmacopeial (USP) Convention quality standards. This means they volunteer to have their products tested. An outside company will check them for quality and purity before they are sold. These supplements display additional credentials on their labels. Look for them to say “USP Verified” or “ConsumerLab.com Approved Quality.”
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. 
Fats: Can they be healthful? Fats get a bad reputation but are necessary for good health. Different sources of food provide different types and amounts of fat. This article looks at which fats are actually good for you and how to go about replacing unhealthy fats with fats that are good for you, as well as the relationship between fat and weight. Read now
To make it easy to find reliable information, NIH has fact sheets on dietary supplements at ods.od.nih.gov/factsheets/list-all/. NIH also recently launched an online Dietary Supplement Label Database at www.dsld.nlm.nih.gov. This free database lets you look up the ingredients of thousands of dietary supplements. It includes information from the label on dosage, health claims and cautions.
Dietary supplements are complex products. The FDA has established good manufacturing practices (GMPs) for dietary supplements to help ensure their identity, purity, strength, and composition. These GMPs are designed to prevent the inclusion of the wrong ingredient, the addition of too much or too little of an ingredient, the possibility of contamination, and the improper packaging and labeling of a product. The FDA periodically inspects facilities that manufacture dietary supplements.