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.

Interglobular dentine in first and third molars: relation to hours of sunshine during growth in two archeological populations from England

Thin ground sections of first molars (M1), third molars (M3), and second premolars (P2) were scanned by light microscopy for relative amounts of interglobular dentine (IGD) in the top half of the crown. Two well-dated cemetery series of English provenance were sampled: the Saint Bride's Church collection (SB) from eighteenth century London, for which the sex, age, and calendar year at death of each individual are known; and the early Anglo-Saxons from Abingdon (A-AS), near Oxford. A lesser number of prehispanic aboriginal Guanche teeth from Tenerife (TG) were also studied. Estimates of insolation in the past were developed indirectly by reference to delta 0(18) mass spectrometer analyses of dated layers of the Greenland ice sheet. In the M1 and M3 of the SB and the A-AS populations, IGD varied as an inverse linear function of average annual hours of bright sunshine below a certain critical level, the insolation deficit threshold being significantly higher and IGD formation faster in the M1 than in the M3. No such dose-response gradient was apparent in the P2 data, presumably because the calcification of this tooth during the fourth year of life coincides with serious pediatric illnesses and weaning of the child onto cereal foods rich in phytate, which together confound and overwhelm the insolation deficit effect. IGD in all three types of teeth of the small TG series was considerably higher than had been predicted on the basis of bright sunshine availability; but the discrepancy is readily explainable in terms of this population's dietary, which relied on barley as the main staple.