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close this bookFood from Dryland Gardens - An Ecological, Nutritional, and Social Approach to Small Scale Household Food Production (CPFE, 1991)
close this folderPart I - Gardens as a development strategy
close this folder2. Gardens and nutrition in drylands
close this folder2.6 Vitamins
View the document(introduction...)
View the document2.6.1 Vitamin A
View the document2.6.2 Vitamin D
View the document2.6.3 Vitamin C
View the document2.6.4 Folacin
View the document2.6.5 Thiamin (B1)
View the document2.6.6 Riboflavin (B2)
View the document2.6.7 Niacin

2.6.2 Vitamin D

FUNCTION This fat-soluble vitamin is important for the regulation of calcium and phosphorus in the body to make strong bones and teeth, especially in infants and children (section 2.7.3). The ultraviolet rays in sunlight cause vitamin D to be formed from a naturally occurring substance in the skin. It is also present in certain foods. Rickets is a disease resulting from vitamin D deficiency and causes softening and malformation of the bones. PROBLEMS IN DRYLANDS In most dryland tropical and subtropical countries there is enough sunlight to supply people’s vitamin D requirements. However, there are vitamin D deficiencies in Ethiopia; in the larger, crowded cities of drylands in the Near East and Asia;37 and where cultural or religious values stress covering most of the body, such as among some Moslems and Hindus.38 Rickets may become a problem during and after weaning if the vitamin D present in breast milk is not replaced by exposure to the sun or supplied by another dietary source.

REQUIREMENTS The amount of sunlight needed to provide someone with their vitamin D requirement depends on the altitude (height above sea level) or latitude (how close to the equator) of where they live, the season, the frequency and length of exposure, and how dark their skin is.39 People with darker skin colors must be exposed longer than those with lighter skin colors. The higher the altitude or the closer to the equator, the less exposure required. The elderly can only synthesize half as much vitamin D from sun exposure as a similar younger person can. It is difficult to set a dietary requirement since diet is not the only source of this nutrient. SOURCES Dryland gardens may contribute in two ways to meeting vitamin D requirements. They can provide eggs whose yolks are a good source. They can also provide a place of seclusion where, while doing other work, mothers can expose a portion of both their own and their baby’s skin to sunlight for a brief period every day. Unless fortified, cow’s milk is not a good source of this vitamin.