After intestinal absorption and cutaneous production, vitamin D3 is transported to the liver where it undergoes initial processing (hydroxylation), the second takes place in the kidneys releasing the active form 1, 25-hydroxyvitamin D3. This hormone reaches the nucleus of target cells and regulates the expression of many genes.
Food containing vitamin D
Food containing the most amount of vitamin D are essentially: halibut, tuna, salmon, herring, anchovies, sardines and mackerel.
Optimal values of vitamin D
Adult values of serum 25-OH vitamin D should be ranged between 30 pg / ml and 100 to 150 pg / ml. A daily dose of 10,000 IU in addition to adequate food intake does not cause side effects (no hypercalcemia).
Upper figure. Representation of nutritional vitamin D amount by Yates et al. The abbreviations represent: EAR; estimated average requirement for vitamin D, AI; adequate intake, UL; upper limit (calculated by dividing NOAEL/ UF), NOAEL; no observed adverse effect level, UF; uncertainty factor, LOAEL; lowest observed adverse level. Middle figure. This graph illustrates a hypothetical situation by combining the upper limit values (UL) with needs assessment vitamin D in adulthood estimated by the data published in 2006. Bottom figure. Represents what the author proposes may be the accepted reality for vitamin D in the future, based on an RDA that reflects the vitamin D supply according to data on the tolerance dose without side effects.
No toxic effects were encountered at concentrations <140 nmol / L, which corresponds to vitamin D intake of 250 microg (10000 IU) / d. Published cases of hypercalcemia due to overdosage of vitamin D involves a daily intake of 25 (OH) vitamin D> or = 1000 microg (40000 IU) / d.
Vitamine D toxicity
Levels up to 100 ng/mL are often seen in individuals with outdoor occupations receiving intense sun exposure without ill effects
Vitamin D intoxication with renal stones and hypercalcemia may be observed when serum levels of 25(OH)D are greater than 150 ng/mL (374 nmol/L). (80)
Roles of vitamin D
1. Keeping blood level of calcium
The role of vitamin D is to maintain blood levels of calcium in the norms in order to preserve cellular functions. 1,25 (OH) 2 vitamin D maintains serum calcium in promoting intestinal calcium absorption and ensures the mobilization and release of calcium stored in bone tissue. Deficiency in vitamin D and / or calcium can lead to a defective bone mineralization which may be responsible for tuberculosis, osteomalacia, osteopenia and osteoporosis.
Vitamin D plays an important role in reducing the risk of breast, colon and ovarian cancer as well as lymphomas of Hodgkin and brain cancers. Vitamin D acts on the tumor microenvironment inhibiting cell proliferation and the formation of new blood vessels (angiogenesis) needed for the growth of the tumor and its spread throughout the body. Vitamin D also induces tumor cell death (apoptosis). The most likely explanation of this effect is related to the antitumor fact that the 1, 25-OH vitamin D control directly and indirectly many genes important for cell cycle, cell differentiation, angiogenesis and apoptosis.
Vitamin D and cancer risk. A large study published in 2007 showed a reduced risk of developing cancer by 75% among those who received supplementation with 1200 IU of vitamin D3 per day.
Vitamin D and breast cancer. A study of 1,760 people showed that levels of 52 ng / ml 25-OH Vitamin D reduces by 50% the risk of breast cancer compared to those who had serum levels less than 13 ng / ml. These serum values correspond to a daily intake of 4000 IU.
Vitamin D and colorectal cancer. Patients with serum 25-OH vitamin D less than 30 pg / mL were approximately twice as likely to develop colon cancer compared to those with higher rates.
Vitamin D and prostate cancer. A study of 19 000 patients during 13 years reveals that patients with plasma levels below 40 pmol / l at inclusion in the study had a 70% risk of developing prostate cancer compared to those who had higher rates. Regarding patients under 52 years the risk was increased by 250% and the risk of developing metastasis was multiplied by 6.3.
Vitamin D and bladder cancer. A study in Finland shows that male smokers whose vitamin D levels in the blood was less than 25 nanomoles per liter had an increased risk of bladder cancer, estimated at 73% compared to participants whose levels were higher to 50 nanomoles per liter.
6. Vitamin D and muscle mass
The vitamin D status is positively associated with muscle strength and physical performance and inversely correlated with the risk of falls. Supplementation of 800 IU of vitamin D administered for 5 months to 124 long-term residents of a nursing home decreased by 72% the risk of falling.
Serum 25-OH vitamin D are inversely related to body fat muscle. Vitamin D deficiency is associated with an infiltration of muscle by adipose tissue in healthy young women.
The rate of 25-OH vitamin D postpubaires girls 16 to 22 years is directly correlated to the size.
7. Vitamin D and cardiovascular disease
Inadequate daily intakes of vitamin D3 actively contribute to the installation and progression of hypertension and cardiovascular diseases particularly among elderly patients with hypovitaminosis D and secondary hyperparathyroidism.
8. Vitamin D and brain
Several mechanisms bind vitamin D to brain development as well as brain function. The brain expression of many genes is affected by treatment with vitamin D. A vitamin D deficiency may be associated with behaviour disorders such as schizophrenia, depression, certain types of dementia (eg Alzheimer’s disease), Parkinson’s disease, a lack of vitamin D can affect learning and memorization.
9. Vitamine D and aging clock
Vitamin D is a potent inhibitor of the proinflammatory response and thereby diminishes turnover of leukocytes (white blood cells). Leukocyte telomere length (LTL) is a predictor of aging-related disease and decreases with each cell cycle and increased inflammation.
Higher vitamin D concentrations, which are easily modifiable through nutritional supplementation, are associated with longer LTL, which underscores the potentially beneficial effects of this hormone on aging and age-related diseases.
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