Vitamin D deficiency has become epidemic for all age groups in Europe and in the United States, causes metabolic bone disease and has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus.

Vitamin D deficiency not only causes rickets among children but also precipitates and exacerbates osteoporosis among adults and causes the painful bone disease osteomalacia.

Very few foods naturally contain vitamin D.
Oily fish such as salmon (360 IU per 3.5-ounce serving), mackerel, and sardines are good sources of vitamin D3.
Although egg yolks are reported to contain vitamin D, amounts are highly variable (usually no more than 50 IU per yolk), and the cholesterol content of egg yolks makes this a poor source of vitamin D.
Cod liver oil is an excellent source of vitamin D3.

Solar ultraviolet B photons are absorbed by 7-dehydrocholesterol in the skin, leading to its transformation to previtamin D3, which is rapidly converted to vitamin D3.
Season, latitude, time of day, skin pigmentation, aging, sunscreen use, and glass all influence the cutaneous production of vitamin D3.

Once formed, vitamin D3 is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form, 1,25-dihydroxyvitamin D3.

Maintaining blood concentrations of 25-hydroxyvitamin D above 80 nmol/L (~30 ng/mL) not only is important for maximizing intestinal calcium absorption but also may be important for providing the extrarenal 1a-hydroxylase that is present in most tissues to produce 1,25-dihydroxyvitamin D3.

Vitamin D3 is fat soluble and is stored in the body fat.
Any excess vitamin D3 that is produced during exposure to sunlight can be stored in the body fat and used during the winter, when little vitamin D3 is produced in the skin.

Researchers recently determined that there was 4-400 ng/g vitamin D2 and vitamin D3 in abdominal fat obtained from obese patients undergoing gastric bypass surgery.

Therefore, for obese individuals, the fat can be an irreversible sink for vitamin D, increasing the risk of vitamin D deficiency.

Scientists observed that, when they gave nonobese and obese subjects a 50 000 IU dose of vitamin D2 orally or exposed them to simulated sunlight in a tanning bed for the same periods of time, the obese subjects exhibited increases in blood vitamin D concentrations of no more than 50%, compared with nonobese individuals.

Monitoring serum 25-hydroxyvitamin D concentrations yearly should help reveal vitamin D deficiencies.

Although chronic excessive exposure to sunlight increases the risk of skin cancer, the avoidance of all direct sun exposure increases the risk of vitamin D deficiency.

Sensible sun exposure (usually 5–10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.

See also:
Biotin (Vitamin B7) may interfere with Lab Tests (2017-11-30)

Low and High Vitamin D Levels in Older Women Associated with Increased Likelihood of Frailty (12/12/2010)

Epicardial adipose tissue inflammation is related to vitamin D deficiency in patients affected by coronary artery disease (2014-10-23)

For more information
The American Journal of Clinical Nutrition
Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease


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