Higher Vitamin D Supplements Advised for Older Black Women


MINEOLA, N.Y., Dec. 7 -- Because dark skin acts as a barrier to sunlight, the vitamin D supplementation recommended for postmenopausal African-American women may need to be higher, according to researchers here.
Action Points --->
Explain to interested patients that this study suggests that postmenopausal black women need higher doses of vitamin D from supplements to achieve recommended serum levels because dark skin blocks sunlight.
Black women who took 20 μg a day (800 IU) instead of the recommended daily allowance of 10 to 15 μg (400-600 IU) had a relatively rapid rise in serum vitamin D compared with a baseline period and a placebo group, John F. Aloia, M.D., of Winthrop University Hospital here, and colleagues reported in the December issue of the American Journal of Clinical Nutrition.
Nevertheless, they added, still higher amounts, ranging from 50 μg/d (2000 IU) to 70 μg/d (2800 IU) may be needed.
Reports of the dose response to vitamin D have been conflicting, and most data were derived from white men and women, while those with dark skin were generally neglected, Dr. Aloia and colleagues said.
To quantify the response in serum 25-hydroxyvitamin D concentrations, the researchers undertook a three-year study that included 208 healthy postmenopausal black women (mean age 60). All women took calcium supplements with a daily intake from all sources of approximately 1,349 mg.
Half the women were randomly assigned to consume a daily placebo, while the other half took 20 μg/d of vitamin D (800 IU) for two years, followed by 50 μg /d (2,000 IU) for another year.
Compared with the baseline period, supplementation with 20 μg/d (800 IU) of vitamin D produced a relatively rapid increase with a mean serum 25(OH)D concentration that rose from a baseline 46.9 ±20.6 nmol/L to 71.4 ±21.5 nmol/L at three months.
During the final year when the vitamin D dose was increased to 50 μg (2000 IU) a day, serum concentrations again rose, but to a lesser extent, 87.3 ±27.0 nmol/L.
Although age, weight, and body fat did not influence a woman's response, a lower baseline measure tended to increase her vitamin D response, the researchers said.
All participants achieved a serum vitamin D concentration >35 nmol/L while 95% achieved a concentration >50 nmol/L. However, they said, only 60% achieved a concentration >75 nmol/L.
The researchers also found a strong positive relationship between vitamin D and serum calcium, which suggested that vitamin D had a potentially positive effect on the availability of calcium to the body. The mean serum calcium concentration among those in the highest quartile of serum vitamin D was 0.25 mg/dL higher than that of those in the lowest quartile (P<0.0001).
However, six women in the vitamin D group had isolated episodes of mild hypercalcemia, which resolved on repeat fasting samples. Similarly, there were isolated episodes of elevated 24-hour urinary calcium excretion in three women, which resolved spontaneously in two participants, while supplements were discontinued in the other woman.
These adverse effects could lead to serious complications, such as kidney stone formation, the investigators noted.
The researchers also reported that they found no influence of increasing vitamin D intake on bone loss. African Americans differ from whites in that they have a more efficient calcium economy, their bone mass is superior to that of whites, and their risk of fracture is therefore lower, the researchers said.
Although the calcium requirement is lower among blacks than it is for white women, the optimal calcium and vitamin D status will be determined in the future by potential extracalcemic effects in protecting against hypertension, obesity, diabetes, autoimmune diseases, and certain cancers, the researchers concluded.
The investigators noted that these results may not apply to other populations. The study took place in a northern latitude so that among light-skinned women or where sun exposure is greater, seasonal adjustments would be a greater consideration.
They also said that their simplified one-measurement, one-dose adjustment algorithm gave satisfactory results, but given individual variability in responses to vitamin D, a better result would be expected if measurements were adjusted a second time.
On the basis of these findings, the researchers suggested an algorithm for prescribing vitamin D in black women. They recommended a dose of 70 μg/d (2800 IU) for those with a concentration >45 nmol/L and a dose of 100 μg/d (4000 IU) for those with a low concentration.
None of the authors reported a conflict of interest.
Primary source: American Journal of Clinical NutritionSource reference:Talward SA, et al "Dose response to vitamin D supplementation among postmenopausal African-American women" Am J Clin Nutr 2007; 86: 1657-1662.