Drs. Narang and Travadi advised parents to allow their infants to sunbathe for the pur- pose of preventing vitamin D deficiency rickets, but recommended that they avoid the period of 10 am to 2
pm(1). Two principles must be noted. First, generation of vitamin l) in the skin requires exposure to UVB rays, since UV A is ineffective for this purpose, It is precisely the midday hours during which UVE rays represent the greatest proportion of overall ultraviolet radiation from the sun. Second, in general only very brief exposures to midday sunlight are sufficient to generate
adequate vitamin D stores. Recommended duration of exposure must depend on latitude and skin pigmentation, but for situations in which vitamin D deficiency is a concern, brief exposure to the sun during midday would be preferable to more extensive expo- sure at other times.
Martin A. Weinstock,
Professor of Dermatology,
Brown University,
Providence, Rhode Island, USA.
