Over the past decade, many studies have revealed the importance of the gut microbiome in disease development and treatment, including in cancer. Because both host genetics and the gut microbiome can influence host phenotype and treatment outcome, there is an urgent need to develop precision medicine and personalize dietary supplementation based on an individual’s microbiome.
The use of dietary supplements is widespread. High doses of vitamins are thought to be helpful because they help the body recover from damage and maintain itself long-term. Many vitamins are not harmful in doses even 10 to 100-fold higher than officially recommended. Some governments warn about possible negative side effects, even including increased mortality from "excessive" intake of certain supplements. However, supplements of essential nutrients have been available for more than 80 years. They are known to be safe, and the observed side effects are generally mild with few exceptions.
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."
Sure, you don't know what you'll be in the mood for later, and will you even be hungry? Yes, probably. After all, increased snacking is one reason behind the rise in calorie intake over the past few decades, according to a 2011 study in PLOS ONE. "When you leave your office to go find something, that's when bad choices are made," says Schapiro. "That's when a hot pretzel, bag of candy, or donut can look very appealing." Make sure your desk (or fridge) is stocked with an emergency stash of snacks, like Greek yogurt, individual packs of nuts, dried fruit, and nitrate-free jerky.
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 VITAL trial showed that neither vitamin D nor fish oil supplementation significantly reduced the incidence of cardiovascular disease (CVD). Conversely, current evidence supports the benefits of multiple dietary patterns, especially the Mediterranean diet, in primary prevention of CVD. Health effects of low-carbohydrate diets depend on the food sources of macronutrients.
As continual research on the properties of supplements accumulates, databases or fact sheets for various supplements are updated regularly, including the Dietary Supplement Label Database, Dietary Supplement Ingredient Database, and Dietary Supplement Facts Sheets of the United States. In Canada where a license is issued when a supplement product has been proven by the manufacturer and government to be safe, effective and of sufficient quality for its recommended use, an eight-digit Natural Product Number is assigned and recorded in a Licensed Natural Health Products Database. The European Food Safety Authority maintains a compendium of botanical ingredients used in manufacturing of dietary supplements.
Total sales for the U.S. dietary supplement industry in 2006 are estimated at $22.1 billion, with vitamins accounting for $7.2 billion of that, says Patrick Rea, editor of the market research publication Nutrition Business Journal. Included in this total are not only sales of vitamins, but also those of minerals, herbs/botanicals, sports supplements, meal supplements, and weight loss products.
If you suspect that you have had a serious reaction from a dietary supplement, let your health care provider know. He or she may report your experience to the FDA. You may also submit a report to the FDA by calling 800-FDA-1088 or completing a form online. In addition, report your reaction to the dietary supplement company by using the contact information on the product label.