"Extraordinarily interesting and happy years": Martha M. Eliot and pediatrics at Yale, 1921-1935

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McCollum Award Lecture, 1994: vitamin D--new horizons for the 21st century

Vitamin D is absolutely essential for the maintenance of a healthy skeleton throughout our lives. There is mounting evidence that vitamin D insufficiency and vitamin D deficiency in elderly people is a silent epidemic that results in bone loss and fractures. It is casual exposure to sunlight that provides most humans with their vitamin D requirement. Seasonal changes, time of day, latitude, aging, sunscreen use, and melanin pigmentation can substantially influence the cutaneous production of vitamin D. Although the recommended dietary allowance for vitamin D in adults is 5 micrograms (200 IU), there is mounting evidence that in the absence of exposure to sunlight the vitamin D requirement is at least 15 micrograms (600 IU)/d. The skin is a target tissue for the active form of vitamin D (1,25-dihydroxycholecalciferol). 1,25-Dihydroxycholecalciferol inhibits the proliferation of cultured keratinocytes and induces them to differentiate. 1,25-Dihydroxycholecalciferol and its analogs have been developed as an effective new therapy for the treatment of the hyperproliferative skin disease psoriasis.

Photosynthesis of vitamin D in the skin: effect of environmental and life-style variables

Exposure to sunlight continues to play a major role in providing adequate vitamin D nutrition for most of the population of the world, including those who live in countries that practice fortification of dairy, margarine, and cereal products with vitamin D. During exposure to sunlight, the high-energy UV photons (290-315 nm) penetrate the epidermis and photolyze 7-dehydrocholesterol (provitamin D3) to previtamin D3. Once formed, previtamin D3 undergoes a thermally induced isomerization to vitamin D3 that takes 2-3 days to reach completion. Melanin effectively competes with provitamin D3 for the UV radiation that enters the epidermis and limits its photolysis to previtamin D3. However, this is not the major factor that prevents excess production of vitamin D in the skin of people who are constantly exposed to sunlight. During the initial exposure to sunlight, provitamin D3 is efficiently converted to previtamin D3. However, because previtamin D3 is photolabile, continued exposure to sunlight causes the isomerization of previtamin D3, principally to lumisterol. Thus, no more than 10-20% of the initial provitamin D3 concentrations ultimately end up as previtamin D3. Aging, sunscreens, seasonal changes, time of day, and latitude also significantly affect the cutaneous production of this vitamin-hormone.

Laissez-faire in research

These were informal remarks in an after-dinner speech about nutritional and pediatric research as it was initiated 50 years ago when the Cincinnati Children's Hospital Research Foundation was opened. Although from the beginning there were "divisions" in the institute, the success of the organization was due to cooperation rather than division and to the freedom of the investigators to alter their directions according to their change of interests and to changes of needs and opportunities. A plea is made to let capable investigators choose their topics and their methods of research; they are most likely to have success when they are left alone and free of outside pressures.

Historical perspectives: food, feeding, and fancies

An historical overview of feeding habits is presented. Effects of food and feeding on human activity through the ages, changes in dietary habits and its effect on health, and beliefs and decisions about eating are reviewed. Lessons to be learned are offered from this historical perspective.