Vitamin D is a hormone made by your skin by exposure to sunlight. At higher latitudes, such as here in the southern part of New Zealand, the sunlight is not very strong for much of the year so vitamin D deficiencies are common, particularly during winter. People with dark skin or those who work indoors are at greater risk of vitamin D deficiency.

Vitamin D is used to aid calcium absorption from the intestine so people with vitamin D deficiency are at risk for developing weak bones. Vitamin D supplements are available on prescription and are usually taken at a dose of one 50 000 unit capsule once a month. Once vitamin D levels return to normal, ongoing supplementation is not always required, however many people benefit from taking an annual course of vitamin D over the three months of winter.