Suspected causes of low vitamin D
"All age groups lack vitamin D in blood" (SN: 3/21/98, p. 182) may confirm fears expressed long ago concerning the rush to low-fat products. Absorption of vitamin D takes place through the intestine's fat-absorbing route, which functions only when fat is present. Therefore, a vitamin supplement taken on rising or just before bedtime, when no fat is available for absorption, will have little impact on vitamin D status. Supplementing fatfree milk with fat-soluble vitamins is useful only if other fat-containing foods are consumed with the milk.
Carolyn C. Cramoy
I've noted a Catch-22 regarding vitamin D. Tufts' Bess Dawson-Hughes told this volunteer participant in her recent milk study that exposure of face and arms to 10 minutes of sunlight daily provides sufficient vitamin D for the body's needs. My dermatologist, warning this senior citizen about melanoma, says keep skin covered while out in the sun and wear sunscreen.
It may be that widespread sunscreen use is a limiting factor in the concentrations of vitamin D found by researchers; but the lack of vitamin D supplements on pharmacy shelves is surely a confounding one.
C. William Burlin
North Chatham, Mass.
Reading carefully, I noticed that these sweeping generalizations had been developed from the hospital visits of 290 people in New England. That New Englanders often need vitamin D supplements was known to my mother in the early 1940s, when she fed me cod liver oil. That people across the country therefore suffer the same lack doesn't follow.
"Stimulating clue hints how lithium works" (SN: 3/14/98, p. 165) refers to a recent publication that provides evidence of the involvement of the neurotransmitter glutamate in lithium's action. My colleagues and I published a paper in 1994 in the same journal (Proceedings of the National Academy of Sciences) showing that glutamate is involved in lithium's action in the cerebral cortex of monkeys and mice. Subsequently, we showed glutamate's involvement in the action of the other approved drug for manic depression, valproic acid.
Regrettably, the authors of the recent report did not refer to our earlier work.
Lowell E. Hokin
Professor of Pharmacology
University of Wisconsin Medical School
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Table of Contents -- May 2, 1998