Vitamin D is fat soluble and exists in several forms with different biological activity. Foods rich in precursors (precursors) of the active form in the body are dairy products, seafood, and liver. Common in the USA, China, and the EU are so-called functional foods, which are food products (most often pasta) enriched artificially with vitamins and trace elements.
The formation of the biologically active form of vitamin D is a multi-step process and goes through physicochemical reactions in the skin, liver, and kidneys. The key is the involvement of ultraviolet light with a wavelength between 280 and 315 nm, which induces structural changes in the inactive precursors of the vitamin. This takes place in the skin covering of the body.
Adequate intake of dietary precursors and exposure to direct sunlight are the mainstays of maintaining physiological levels of vitamin D in the body. The recommended daily intake of vitamin D with food is 400 international units (IU) for the breastfeeding period and 600 IU for all age groups up to 50 years of age.
Vitamin D is involved in the maintenance of calcium-phosphate metabolism in the body. It regulates the levels of calcium and phosphate ions in the blood and the mineral composition of the bones. Studies in recent years have proven at the molecular level that vitamin D interferes with immune mechanisms as well as cell growth and differentiation.
Studies of vitamin D levels among different age groups and patient populations have demonstrated a high percentage of people with vitamin D deficiency, both with increasing age and with various pathological processes. Associations and hypotheses were made about the relationship of deficiency with the development of oncological diseases, increased susceptibility to infections, autoimmune diseases, etc.
The main question before the scientific community is what is the weight of this deficiency as a risk factor for the onset and development of various diseases and does supplementation with the vitamin (in the form of drops, tablets, functional foods) reduce the oncological risk? Only the results of representative clinical trials can reliably answer these questions.
The largest clinical trial to evaluate the preventive role of vitamin D was conducted in the United States by the Woman’s Health Initiative (WHI) among 36,282 postmenopausal women. They were divided into two arms. Women in one arm received a combination of vitamin D (400 IU) and calcium (1000 mg) daily, women in the other arm received a placebo. The results of the study demonstrated that the combination used did not have a prophylactic role in reducing the incidence of breast cancer and colon cancer among these women.
Trials have also been conducted to evaluate the preventive role of calcium supplementation (the main micronutrient regulated by vitamin D) in relation to the risk of developing colorectal adenomas and colon cancer. The results of Baron et al. showed a statistically significant benefit for people taking 1,200 mg of calcium daily compared to those taking a placebo.
There are no other sufficiently representative studies to demonstrate the benefit of vitamin D and/or calcium supplementation. There are some small trials that even show the opposite – an association of high levels of vitamin D with an increased incidence of pancreatic cancer.
The VITAL trial is currently underway among 20,000 participants, which evaluates the preventive role of the combination of vitamin D and omega-3 fatty acids in relation to some common locations of oncological diseases.
Vitamin D can be obtained in adequate and physiologically normal amounts through a complete diet. There is no scientific evidence that supplementation with an existing deficiency would have a prophylactic role in the development of cancer.