In the southern hemisphere we generally have a surfeit of sunshine - we slap on sun block or don hats when going outside. But in northern climes it’s often the opposite. Many people living in North America, northern Europe and the Scandinavian countries suffer from what’s known as seasonal affective disorder (SAD). It’s a mood disorder and its symptoms are insomnia, reduced attention span and a lack of energy.

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SAD has spawned a number of bad puns, as well as so-called light cafés, where wan bohemians sip latté under fluorescent tubes that mimic daylight. SAD was detected around 1845, but it wasn't recognised as a disorder by psychiatrists until the early 1980s. The National Mental Health Association in the US estimates that it affects around 20 million Americans. Its symptoms read like a to-do list for a long, cold winter: excessive eating, sleeping and weight gain, a craving for starchy, sugary foods.

Extreme cases sound like a serious dose of cabin fever, the edgy, irritable, side-effect of being in a confined space with people who listen to country music or want you to play Monopoly: anxiety, loss of energy, loss of interest in sex, and difficulty in concentrating and processing information.

SAD is caused by a vitamin D deficiency. Vitamin D is converted to its active form by the body in two steps - first in the liver and then in the kidneys. In its active form, vitamin D acts as a hormone to regulate calcium absorption from the intestine and to regulate levels of calcium and phosphate in the bones.

When the body is deficient in vitamin D, it’s unable to regulate calcium and phosphate levels. If the blood levels of these minerals become low, the other body hormones may stimulate release of calcium and phosphate from the bones into the bloodstream. This can lead to a loss of bone density.

Children born with low levels of calcium may develop rickets, a progressive softening and weakening of the bone structure. In severe cases, cysts may develop in the bones.

Rickets is fairly rare, but still occurs in some poor, rural areas. It’s usually seen in young children 6 to 24 months old. Breastfed babies who get regular exposure to sunlight are unlikely to develop rickets.

A vitamin D deficiency among older adults – especially women – can contribute to osteoporosis. Maintaining healthy levels of vitamin can reduce your chances of colon cancer and may help reduce the effects of Alzheimer’s disease.

- (William Smook, Health24)
 

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