- For Adults, the 5 mcg (200 IU) Vitamin D recommended dietary allowance may prevent Osteomalacia in the adsence of sunlight, but more is needed to help prevent osteoporosis & secondary hyperparathyroidism.
- Other benefits of Vitamin D supplemetation are inplicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis and hypertension.
- Total Body sun exposure easily provides the equivalent of 200 mcg (10 000 IU) Vitamin D per day. In contrast, we modern humans usually cover all except about 5 % of our skin surface & it is rare for us to spend time in unshielded sunlight.
- To ensure that serum 25 (OH) D concentrations exceed 100 nmol/L. a total Vitamin D supply of 100 mcg (4000IU) per day is required.
- before 1997, the recommended dietary allowance of Vitamin D for infant & children was 10 mcg (400 IU). In essence, the scientific basic for this dose was that it approximated what was in a teaspoon (5mL) of cod-liver oil & had long been considered safe & effective in preventing Rickets.
- The objective way to assess Vitamin D nutritional status is through the circulating 25 (OH) D concentration.
- Concentration less than 20 - 25 nmol/L indicate severe Vitamin D deficiency; which will lead to rickets & histologically evident osteomalacia.
- Concentrations between 25 & 40 nmol/L reflect marginal Vitamin D deficiency.
- All 25(OH) D values are presented as nmol/L. ( 1 nmol/L = 1 ng/mL X 2.5 )
- Vitamin D has a half life > 1 or 2 months.
- Amounts of Vitamin D are given in mcg, each being equivalence to 40 IU or 2.6 nmol Vitamin D3.
- However, Vitamin D2 is less effective at raising serum 25(OH) D concentrations than is Vitamin D3.
- Sunshine alone can bring 25 (OH) D concentration to 210 nmol/L in normal people & Vitamin D intake of 30 mcg (1200 IU) per day contribute only a negligible fraction of this.
- At least 4 studies support the concept that one full-body exposure to sunlight can be equivalent to an oral Vitamin D intake of 250 mcg (10 000 IU). They calculated a production of Vitamin D in the skin equivalent to 0.045 nmol.d-1.cm-2 expose skin. This equivalent to 10.9 mcg (435 IU) Vitamin D per day for 5 % of skin surface.
- Upper levels of Vitamin D intake were set at 50 mcg per day (2000 IU per day) for all ages. Some individuals would require higher levels than these to achieve serum 25-hydroxyvitamin D concentrations for optimal Calcuim absorption.
- The normal range of serum 25-hydroxyvitamin D concentration is broad at 25-137.5 nmol/L.
- Calcuium absorption efficiency increase with serum 25-hydroxyvitamin D concentration until levels of 80-90 nmol/L were achieved.
- Vitamin D deficient individuals may require Vitamin D intakes that exceed the current upper levels to achieve serum 25-hydroxyvitamin D concentration of >= 80 nmol/L.
- Recommended that serum 25(OH) D should exceed 75 nmol/L in person with osteoarthritis of the knee.
- From what is known now, there is no practical difference whether Vitamin D is required from ultraviolet exposed skin or through the diet.
Risk Assessment for Vitamin D
- Cholecalciferol (Vitamin D3) is produced naturally in human skin exposed to untraviolet-B light. It occurs in some animal products and is added to various dietary supplements (such as multivitamins) and fortified foods (such as milk).
- One IU of Vitamin D is defined as the activity produced by 0.025 mcg Cholecalciferol in bioassays with rats. Vitamin D3 is generally considered to be the primary form of dietary Vitamin D, although ergocalciferol (Vitamin D2), a secondary form, is derived from the yeast & plant sterol precursor, ergosterol.
- Both Calciferols appears to be absorbed with equal efficiency, but Vitamin D2 may be less potent & may have a different toxicological profile.
Adverse Effect Reports
- Excessive Vitamin D intake is associated with additional significant clinical adverse effects, including pain, conjunctivitis, anorexia, fever, chills, thirst, vomitting & weight loss.
- Hypercalcemia due to Vitamin D intoxication per se is always accompanied by serum 25(OH) D concentration > 220 nmol/L.
- Numerous reports of accidental or unimformed consumption of vey high doses of vitamin D:
- Over 4 days period (15 000 mcg/day) develop resistant hypercalcemia & hypertension.
- 42 000 mcg/day for several months resulting hypercalcemia included pain, conjunctivitis, anorexia, fever, chills, thirst, vomitting & weight loss.
- Patient with severe osteoporosis had a Vitamin D intake of 1250 mcg/day and get hypercalcemia.
- Patient with nephritic syndrame, hypertension, and renal insufficiency being treated with hydrocholorothizide develop hypercalcemia while taking 1250 mcg Vitamin D2 per week.
- Patient with history of hypertension treated with hydrocholorothizide & Alpha-methyldopa develop hypercalcemia while been treated with prednisone & taking 1250 mcg Vitamin D per day.
