Vitamin D is a group of fat-soluble steroid-like biochemicals that have one known responsibility in human health–enhancing intestinal absorption of calcium and phosphate, minerals which are necessary for bone development and bone health. In humans, the most important D vitamins are vitamin D3 and vitamin D2, both of which can be ingested from dietary sources, including fishes, milk products, and many other foods. However, the body can synthesize vitamin D’s in the skin when exposure to sunlight is adequate. Because humans can produce their own vitamin D, it is not strictly considered an essential dietary vitamin, which are vitamins that cannot be synthesized in sufficient quantities by an organism, and must be obtained from its diet.
Even though supplementation is necessary for people who aren’t receiving adequate levels of vitamin D through either sun exposure or diet, excessive intake of the vitamin causes a condition called hypervitaminosis D. Excessive vitamin D can lead to acute problems, like excess thirst or increased urination, but over a long-term can lead to heart disease and other chronic conditions.
Other than eliminating direct risks, are there things that can be done to actually prevent “cancer”? Once again, with over 200 types of cancer, this may be an impossibility, but the three most popular cancer prevention ideas are diet, vitamins and other types of nutritional supplements. Vitamins and other supplements are a $61 billion industry in the US. They generate these sales with minimal regulation, minimal quality control over the quality and dosage, and no requirement to actually provide evidence that the supplements do what is claimed by the supplement industry, aka Big Herbal. The FDA only gets involved with the industry if there’s some dangerous side effect, or when the claims of the industry are so outrageous that the FDA has no choice but to get involved.