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As the sun blasts the South in this year's long and hot summer, the short days of winter seem a long way away.
But, of course, the cycle of the seasons turns and already the occasional tree displays a hint of autumn. Before long winter will have us in its grip.
Not only do the hours of daylight shrink but the sun's angle through the atmosphere also changes. Instead of seeking shelter from its rays, instead of skin being fried, instead of covering up, we are actually encouraged to seek exposure in moderation.
The dangers of vitamin D deficiency have been well known in the north of the northern hemisphere for many years, so much so that children in Scotland are dosed with supplements. Vitamin D, the ''sunshine vitamin'', is vital for bone health and the best known deficiency malady is rickets. In serious childhood cases it causes bowed legs, stunted growth and intellectual impairment. It was common in the West into the last century.
In recent years, however, increasing concern has again been raised about vitamin D deficiency, both in mild and more serious forms.
University of Otago researchers this week announced findings that add weight to disquiet. Their study followed 126 women who gave birth in Dunedin between 2011 and 2013. Vitamin D deficiency rates were 65% for mothers and 76% for infants, rising to as high as 90% for infants in winter. There was even evidence of rickets in three infants.
Study co-author Ben Wheeler said the study, and an earlier one he referenced, suggested vitamin D deficiency was much more common than previously thought.
It would also seem to extend well beyond at-risk groups - for example vegans (vitamin D is found in the likes of oily fish, liver, cheese and egg yolks) and Muslim women who cover up or people with very dark skin.
Modern lifestyles, often with little time outdoors, and covering up in clothing all increase the risk of vitamin D deficiency.
Dr Wheeler goes so far as proposing at the very least vitamin D supplements should be recommended in the South.
The Ministry of Health at present advises doctors only to consider use of supplements, advice Dr Wheeler calls very weak.
He says a GP or maternity provider in the South Island should be recommending all women receive supplements. Women could then make their own decisions, as with all recommendations.
The reluctance of authorities to come out more strongly could well be because of the perils of skin cancer and the fear of mixed messages - on the one hand sun is bad, and on the other, good.
The ministry does, nonetheless, have sensible guidelines, not shying away from the dangers of summer sun through the middle of the day.
It says if you live in the South Island (especially south of Nelson-Marlborough) and get little time outdoors in the middle of the day between May and August, you may be at risk of vitamin D deficiency in spring. You may wish to consider taking vitamin D tablets during these months.
It also recommends a daily walk or another form of outdoor physical activity around the middle of the day during those months. As we all know, it can be too easy in the middle of winter not to venture outside during the day and, for many workers, that can mean going to work and going home again in the dark.
Not surprisingly, those in rest-homes are at high risk of deficiency, accentuated because the ability to produce the vitamin in the skin decreases with ageing.
The message about the importance of vitamin D in New Zealand is gaining ground steadily. The latest research is a timely addition to this information. New Zealanders willing to take an active interest in their health should take heed while, at the same time, acting on the crucial ''sunsmart'' warning for much of the year. We must not forget that about 380 New Zealanders a year die from skin cancer.