Think of sunshine and you're likely to think of skin cancer. But the sun's rays - the main source of vitamin D - are vital for our health and wellbeing, and do far more good than harm.
Even when we're developing in the womb, a vitamin D deficiency in the mother can cause us growth problems, skeletal deformities, and an increase in the risk of hip fractures later on.
When we grow up, a vitamin D deficiency can trigger osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases, and heart problems.
Without the vitamin, only about 10 per cent of dietary calcium and 60 per cent of phosphorus gets absorbed by the body, and these are nutrients that are vital for bone mineral density.
People who live at high altitudes, where the sun's rays fall at such an angle that they cannot produce adequate amounts of vitamin D, are more likely to develop Hodgkin's lymphoma, and cancers such as colon, pancreatic, prostate, ovarian and breast.
Dr Michael Hollick, from the Boston University School of Medicine, recommends that the recommended daily intake of vitamin D should be increased to 1000 IUs.
He believes the best strategy to achieve this is a combined one of sunshine - but only so that it slightly reddens the skin - more oily fish in our diet, and supplements.
(Source: New England Journal of Medicine, 2007; 357: 266-81).