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I found your two articles on vitamin D very interesting. My question now is whether the rays received in a tanning bed can cause the skin to manufacture vitamin D.

Wendy Wade
Kalamazoo, Mich.

Ultraviolet–B radiation triggers the skin to produce vitamin D, whether those rays come from the sun or a lamp. However, not all tanning salons use lamps that emit UV-B rays as well as UV-A wavelengths .—J. Raloff Two thoughts on vitamin D: Are treatments for seasonal affective mood disorders, involving shining bright lights on the skin, effective simply because they stimulate the production of vitamin D? Does exposure to sunlight affect blood-cholesterol levels?

Steve Palmer
Plainfield, N.J.

Could the lack of vitamin D be a cause of the “death in the dark months” of elderly people? The rise of depression in the winter months could be accounted for, as well, and perhaps treated very simply by adding the vitamin to our diets. Follow up, please.

Karl L. Roesch
Arlee, Mont.