Miriam Polunin investigates SAD.

Most people have by now have heard of SAD, Seasonally Affected Disorder, as a result of which sufferers are plunged into often near suicidal depression by winter darkness However, there is now substantial, though not conclusive evidence, that many people who aren’t officially  'SAD' can also feel better by upping their light supply in winter.

It’s no news that UK humans crave sun. But what many of us may not realise is that it isn’t the heat of the sun we chase, but the light. We know that light. Deeply affects several body systems. Light helps regulate our body clocks, suppressing the hormone melatonin  (that makes us drowsy) and other hormone systems for the night. Light influences our production of the neurotransmitter serotonin which enhances mood (Prozac works by boosting serotonin levels) but light’s effects depend on its quality, timing and quality.

The quality of natural light most people receive has dived over the last 80 years. The gradual spread of artificial lighting after Edison’s first light bulb in 1879 meant people no longer sought out daylight. Trains, buses and cars reduce the time people spend walking outdoors. Mechanised and chemical-dependent to agriculture took millions away from fieldwork. Now the 24/7 societies threatens to take even more light out of our lives as more people than ever work shifts that mean they need to sleep during daylight.  Researchers estimate that even well lit offices only provide around 500 lox (the most used measure of light strength) and typical homes 100 lox. That’s at least 20 times lower than the level of light on a sunny day.

The best solution to the lack of light is to spend time outdoors. As it’s the light that enters the eyes that affects our melatonin system. Avoid dark glasses. If light is glaring shade eyes. You’ll still be receiving light at a slower rate. You can protect your skin with sun filters, and you don’t need to strip off, so risk from UV rays is small. Alternatively, there are light boxes.

No one knows how much light you need to prevent health problems developing. However trails of light – boxes suggest that a minimum of 2.500 lox – five times the typical well-lit office – is needed to affect melatonin or scooting levels.

The stronger the light box, the less time you need to sit in front of it, and the further you can sit from it. There are at least 20 different models on sale. You might choose sitting just 30 minutes a mere 25cm from 10.000 lux light box, or prefer a smaller 2.500 lux box at arm’s length (or on top of you computer) for around two hours. There is also a light visor, powered by rechargeable batteries, that leaves you free to walk around while light beams to your retina. The closer and longer you are willing to be near your light, the less powerful the model you need and the less it will cost.

Use extra light in the morning to switch off drowsy-making melatonin and allow other hormones to rise. Do this, and save time with a bedside light that simulates dawn gradally switching off melatonin so you wake up more alert, for general mood and wellbeing it seems morning or afternoon use of light boxes is equally effective. Improvement is usually, within four to 10 days of starting.

Light experts are also concerned with the quality of everyday light. If daylight is the ideal most artificial lights are very far from it. Compared to cool, almost white daylight, tungsten light bulbs produce too much red and orange. Halogen lights are a little better. The main problem of fluorescent lights (including low energy bulbs) is their never ending flickering. But they also have too much blue and green. Choosing light bulbs, which simulate daylight, solves most of these problems. Limited trails in offices and schools show that (Almost) full spectrum light improves wellbeing and reduces eyestrain. Full spectrum light naturally includes the ultraviolet parts of the spectrum but light boxes screen out virtually all the skin cancer causing UV parts of the light.
  
Our need for Vitamin D is a main reason why light boxes can never replace time outdoors. UV sunlight – not necessarily bright sun- absorbed by our skin produces 80 to 90% of our vitamin D, while food sources are few, Vitamin D is not only essential for the absorption of calcium for strong bones and teeth, but is also involved in several other body functions. Including immunity – and mood. In Britain there is no UV radiation of the light wavelength to produce vitamin D from the end of October to the end of March. Vitamin D can be stored in the body from the summer – but only if you had more than you needed the. Trousers and sun – block don’t help. There’s increasing concern that fear of skin cancer may be leading to growing vitamin D deficiencies so unless you spend most of your time outdoors, winter vitamin D supplements are advisable.

If you regularly spend time outdoors, your skin will tan gradually, giving some natural protection against UV rays, If you worry about possible damaging effects avoid peak UV hours (11am-3pm) and make sure you eat plenty of foods rich in Vitamins C and E.

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First Published in 2002