Vitamin D - Sunshine Vitamin / Antioxidant against health problems - Factors affect D3 availability /conversion
Factors Affecting D3 Availablility
and Conversion in the Body
Insufficient dietary fat - vitamin D
is a fat-soluble vitamin and thus requires some dietary fat for conversion.
Conversion may also be inhibited by damaged fats (E.g.
trans fats).
Certain medical
conditions may prevent dietary fat absorption - E.g. pancreatic enzyme deficiency, IBD (such as Crohn's and
Whipple's disease), celiac disease, cystic fibrosis, gall bladder or liver
disease, partial/total removal of stomach or intestines. Symptoms of fat
malabsorption include diarrhea and greasy stools.
Skin Color -A higher melanin content in darker skin reduces
D3 production. A tan is the skin's inbuilt
protection against producing too much vitamin D.African Americans and other dark-skinned persons who do not get
sufficient sun exposure, are at a high risk for
vitamin D deficiency.
Parathyroid gland or
Kidney Diseases –impair synthesis of
CALCITRIOL, the active form of
vitamin D.
Aging –production of vitamin D precursors (7-dehydro-cholesterol)
and Kidneys'conversion ability diminishes with age. A 70 year old has only 25% of
the capacity of a young adult to produce vitamin D3.
MacLaughlin J, Holick MF, Aging decreases the capacity ofhuman skin to produce vitamin D3, J. Clin Invest 1985, 76:1536-1538.
However,
the elderly are still able to satisfy their vitamin
D needs by going into the sun
Davie M, et al, 1980; Holick MF, Vitamin D
deficiency, N. Eng J Med 2007; 357:266-281
or by utilizing a
full-spectrum tanning bed.
Tangpricha V et al, Tanning is associated with optimal vitamin D
status and higher bone mineral density, Am J Clin Nutr, 2004
Sunscreen –an SPF of 8 has the capacity to reduce
D3 production in the skin by 95%
Obesity –in one study, when exposed to the same amount of natural sunlight,
obese subjects produced only about half the amount of
vitamin D3 as normal weight subjects.The study concluded that vitamin D
insufficiency is likelydue
to the decreased bioavailability of vitamin D3 from
cutaneousand
dietary sources because of its deposition in body fat compartments
Wortsman J, et al, Decreased
bioavailability of vitamin D in obesity, Am. J. of Clin. Nutr., 72(32):690-693,
2000
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