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As a cold blast from the south slowly abates - winter's envoy, with a taste of things to come - some of us might be expected to experience a perhaps imperceptible change of mood. From the buoyant "sunny" optimism of an Indian summer which, when the figures are compiled, will mark down April 2012 as the sunniest on record in Dunedin, to the dark, cold grim days of August, there may be a slow slide to a low-level of generalised "gloom".
In short, there may be those among us who become unduly SAD, suffering from the now well-recognised Seasonal Affective Disorder. The winter blues have, anecdotally at least, been around for ages. In the 1980s, the condition was given a name and systematically studied and described by United States mental health physicians.
Among their discoveries was that the reduction in light - particularly in some of the longer and darker northern winters - affected mood most probably by interaction with the body's hormone production (or lack thereof): a reduction in the "happy" hormone serotonin for example, or perhaps a stimulation of melatonin.
And while SAD is now thought to affect up to about 6% of the US population, a milder "subsyndromal" form of the disorder - "blues" rather than "depression" - has been measured as afflicting up to about 14% of us. The common prescription for the latter variety has long been to seek higher levels of solar exposure through increased outdoor activity and exercise on sunny days.
In this country, such a prescription raises the scientific temperatures in a different sun-exposure debate, one which, at its extremes, pits the benefits of Vitamin D against the risks of skin cancer.
Vitamin D is produced in the body through exposure of the skin to the sun, or more specifically, to ultraviolet B (UVB) radiation. It is also found in food such as fatty fish and eggs, and some choose to maintain levels though dietary supplements.
There have been arguments that the pendulum against cancer-promoting sun exposure has swung too far: while necessary public health campaigns have emphasised the need to cover up under the sun and reduce direct or prolonged exposure to New Zealand's fierce UV radiation, has the reduction in UVB begun to manifest itself in an upswing of other maladies?
The links between Vitamin D and good bone and muscle strength and function are well-known. Vitamin D deficiency can lead to a thinning of the bones - osteoporosis - which in turn can increase the risk of breakages and fractures. However, recent scientific and medical discoveries suggest that the vitamin can and does play a role in a host of other diseases.
There are now studies under way investigating possible links between Vitamin D levels and autoimmune disorders, colorectal cancer, as well as respiratory and cardiovascular disease.
It will take some time, potentially years, to tease out the doubtless complex nature of such inter-relationships, but in the meantime it may be necessary to approach the issue of sun exposure with a degree more sophistication than has been evident over the last decade or two.
Last month, in an attempt to address the confusion in some quarters as to the appropriate amount of sun exposure, the Ministry of Health, the Cancer Society, and ACC issued new guidelines on Vitamin D and sun exposure which, among other things, recommended outdoor activity between the months September and April should preferably take place in the early morning or later in the day, while for the rest of the year around the middle of the day is preferable.
These are the shades of grey, the cautionary finer points, in a discussion about the sun and how it affects us. Most of us do not need a public health policy document to know, however, that when sun shines, the mood lifts and when it shines for prolonged periods of time we tend to live in a happier place. The changes in seasons, the onset of autumn, the arrival of lowering skies, of rain and sleet and snow may be natural and necessary, but April sun, as this past month attests, does not exist only in Cuba - and it can be a wonderful curative.