Vitamin D — traditionally, it has been associated with the body's use of calcium. Deficiency has been associated with rickets. More recent research is showing that deficiency can increase the risk of such such a diverse range of maladies as diabetes, dementia, schizophrenia & falls in the elderly.
In some ways, the ability of the skin to produce vitamin D when exposed to sunlight provides a simple solution. Except, sunlight exposure carries with it elevated risk of skin cancer. Sunscreen provides a level of protection against sunburn & skin cancer, but also prevents production of vitamin D. Dark skin is protective against skin cancer, but also reduces vitamin D production. At high latitudes, a dark skin may make it difficult or impossible to get enough sunlight exposure.
In the light of the above, dietary sources & supplements become more attractive. Relatively few foods contain vitamin D, but fatty fish (such as salmon & tuna) & fish liver oils are among the best sources. Lesser sources are beef liver, cheese, & egg yolks.
Low vitamin D linked to diabetes
http://www.newscientist.com/article/dn1511-low-vitamin-d-linked-to-diabetes.html#.U-cJ1NB_W2c
Lack of vitamin D more than doubles risk of dementia
http://www.newscientist.com/article/dn26022-lack-of-vitamin-d-more-than-doubles-risk-of-dementia.html#.U-cLO9B_W2c
Elderly falls linked to vitamin D deficiency
http://www.newscientist.com/article/dn4433-elderly-falls-linked-to-vitamin-deficiency.html#.U-cL_tB_W2c
Vitamin D deficiency & increased risk of schizophrenia
http://www.medicalnewstoday.com/articles/279915.php / children childhood diet lacking in vitamin D develop type 1 diabetes Finland Finnish researchers supplements disease type 1 diabetes autoimmune disease immune system cells insulin producing cells pancreas populations children Asian descent UK deficient in vitamin D childhood obesity infection enterovirus childhood obesity vitamin D elderly people increased risk dementia Alzheimer's disease study investigate links vitamin D deficiency dementia, risk dementia Alzheimer's disease David Llewellyn University of Exeter Medical School UK lowest levels vitamin D higher risk chances developing schizophrenia sunny born new research theory vitamin D deficiency during pregnancy lack of sunlight alter development child's brain womb data link schizophrenia vitamin D deficiency common epidemiological trends develop schizophrenia Europe North America born spring four times more likely to be born to Afro-Caribbean immigrants sunlight make vitamin D dark darker skin pale paler skinned people John McGrath Queensland Centre for Schizophrenia Research Wacol lack of vitamin D during early development schizophrenia /
