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.
Eat a balance of carbohydrates, proteins and fats at each meal and choose foods rich in fiber, vitamins and minerals. A good way to do this is to fill your plate with 3–4 food groups at each meal. Eat a combination of protein-rich foods, whole grains, dairy, fruits and vegetables, and incorporate the groups you miss into other meals and snacks throughout the day. Stick to healthy portions — see our Essential Guide to Portion Sizes for tips.
Your doctor may also be able to notify you of any other potential risks a supplement might pose to your health (especially if you're pregnant, have other medical conditions or are planning to have surgery), as well as offer guidance on the best dosage to take. If your doctor isn't comfortable with advising you on supplement use, ask if he or she can refer you to a qualified supplement-savvy health practitioner. But keep in mind that because of a lack of research on side effects, just how a supplement may interact with a medication isn't known.
Nutritional supplements may be designed to provide specialized support for athletes. Some of these consist of high-protein products, such as amino acid supplements, while other products contain nutrients that support metabolism, energy, and athletic performance and recovery. People engaging in intense athletic activity may have increased needs for water-soluble vitamins, antioxidants, and certain minerals, including chromium. Sports drinks contain blends of electrolytes (salts) that the body loses during exertion and sweating, as well as vitamins, minerals, and performance-supporting herbs.
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.
^ Siscovick DS, Barringer TA, Fretts AM, Wu JH, Lichtenstein AH, Costello RB, Kris-Etherton PM, Jacobson TA, Engler MB, Alger HM, Appel LJ, Mozaffarian D (2017). "Omega-3 Polyunsaturated Fatty Acid (Fish Oil) Supplementation and the Prevention of Clinical Cardiovascular Disease: A Science Advisory From the American Heart Association". Circulation. 135 (15): e867–e884. doi:10.1161/CIR.0000000000000482. PMID 28289069.
In the United States, the Dietary Supplement Health and Education Act of 1994 provides this description: "The Dietary Supplement Health and Education Act of 1994 (DSHEA) defines the term “dietary supplement” to mean a product (other than tobacco) intended to supplement the diet that bears or contains one or more of the following dietary ingredients: a vitamin, a mineral, an herb or other botanical, an amino acid, a dietary substance for use by man to supplement the diet by increasing the total dietary intake, or a concentrate, metabolite, constituent, extract, or combination of any of the aforementioned ingredients. Furthermore, a dietary supplement must be labeled as a dietary supplement and be intended for ingestion and must not be represented for use as conventional food or as a sole item of a meal or of the diet. In addition, a dietary supplement cannot be approved or authorized for investigation as a new drug, antibiotic, or biologic, unless it was marketed as a food or a dietary supplement before such approval or authorization. Under DSHEA, dietary supplements are deemed to be food, except for purposes of the drug definition."
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.
The essential nutrient minerals for humans, listed in order by weight needed to be at the Recommended Dietary Allowance or Adequate Intake are potassium, chlorine, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, selenium and cobalt (the last as a component of vitamin B12). There are other minerals which are essential for some plants and animals, but may or may not be essential for humans, such as boron and silicon. Essential and purportedly essential minerals are marketed as dietary supplements, individually and in combination with vitamins and other minerals.
I have identified a number of arguments in favor of supplementing the modern diet with essential nutrients, here summarized with 7 headlines. Most people should consider taking a multivitamin supplement containing vitamins and minerals even if they eat a nutritionally balanced diet. Additional nutrients may contribute to better health and, in some cases, can be of vital importance in our modern world. The arguments are presented in random order, i.e. the order does not reflect priority.
Eat healthy fats. According to the American Heart Association, women should get at least five to 10 percent of total daily calories from omega-6 fatty acids (equal to 12 to 20 grams), and between 0.5 and 3 grams of omega-3 fatty acids, depending on individual risk for heart disease. Good sources of omega-6 fatty acids include sunflower, safflower, corn, cottonseed and soybean oils. And good sources of omega-3 fatty acids include fatty fish, tofu and other forms of soybeans, canola, walnuts, flaxseed, and their oils. Talk with your health care professional about how much of these beneficial oils you should be getting, how you can best incorporate them into your diet and whether or not you should be taking them in supplement form.
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.