I've held off contributing to the discussion on Vit D and skin exposure to sunlight, hoping others from very sunny climates would contribute.
    CLIMATE:  Now, I am aware of the literature about Vit D deficiency and rickets in breastfed infants, even in sunny climates, much of the cases series involving cultures with limited skin exposure for cultural or religious reasons, and dark skins.  Where I live now, and in the even hotter places where I spent most of my life, *over-expsoure* to sunlight is a bigger issue.  This state, Queensland, has reputedly the highest incidence of skin cancers in the world (mainly basal cell and squamous cell) attributed to excess sun exposure, especially with early sunburn damage to delicate skins early in life.  
    CULTURE:  Two or three generations ago, it was customary for people of European origin to war shady hats and long sleeve and long skirts (or trousers for the men) when outdoors.  A study in the early 1960s (sorry, I don't have details) showed that the older Queensland men of Caucasian origin who had done outdoor work all their lives had very little skin damage and very few early skin cancers.  These were on the backs of their hands and the tops of their ears, areas exposed to the sun.  Later generations followed the fashion for short trousers, short-sleeved or sleeveless shirts (or no shirts for some men and midriff tops for young women) and certainly hats were not considered "cool".
    SKIN TYPE:  Increased sun exposure was combined with a further risk factor - somewhere round 30% of Australians have substantial Celtic heritage, with fair skins, i.e. with less pigment.
    To give a personal example, my father and brother both had auburn hair and sun-sensitive skins.  Dad sued to play a lot of sport (criicket) in his youth though he largely gave that up after marryign at age 50.  He rode a bicycle and did a lot of walking.  He always wore the customary suit, originally an unfashionable white one, and on informal occasiona a long-sleeved shirt.  The one time I knew him to go out in a short-sleeved shirt he sunburnt, even through the shirt, and I once saw him sunburn when resting in a hammock in the shade with a hat over his face, because of reflected light. (He only did that once.)  He always wore a hat outdoors.  He died at 76 with not a trace of skin cancer.  Although my mogtehr was strict about staying out of the sun in the middle of the day and wearing hats, my brother came to adolescence and adulthood when short sleeves and short pants became usual.  He stopped wearing a hat.  He did some sailing on weekends for a very few years (too much severe sunburn) and didn't play other sport.  By middle-age, he was starting to have skin cancers on his legs, arms and face.  I have no idea how many he has had cut out of him - a lot.
    The old idea of "sunbaths" for babies is considered risky in our part of the world - with the common skin type, enough sunlight for vit. D synthesis being obtained in daily activities, going from house to car or carpark to shops, etc.  This hasn't filtered down to grassroots health staff and families.  A recent article in an Australian paediatric journal last year examined advice and attitudes of health-care staff as regards sun exposure of infants, and epressed concern at the lack of knowledge of the issues.  Some health-care staff were recommending sun exposure for vit D, to resolve jaundice (without an evidence base) and for nappy (diaper) rash.  The authors were from the Skin Cancer Research Group at the School of Public Health & Tropical Medicine at James Cook University in Townsville.  Publication details are:

Harrison Sl, Buettner PG, MacLennan R. Why do mothers still sun their infantrs?  J Paediatr Child Health 1999;35(3):296-299.

Those of you working in the Tropics or sub-tropics, or planning to work in these climates, might like to check your library for a copy of the article.
    By the way, in England, the Tor Bay (Devon) Skin Cancer Study, published in the BMJ (from memory) in the early 1990s (probably mid-1992?) checked the skins of a large number of people on the beaches of Tor Bay in the summer.  Two malignant melanomas and a number of pre-cancerous skin changes wre identified.  This, again, is in a very fair-skinned population, with a common belief that getting lots of sun exposure is "healthy"  And this is south-west England, not the Tropics. "Moderation in all things and in all things moderation"? might be a good motto.
    I present this information to emphasise the interplay of a number of factors - climate, skin type, and culture (as regards amount of skin exposure and lifestyle)
    Virginia
    in Brisbane, Queensland

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