When it's cold and miserable outside, my thoughts often turn to the time I was a family doctor in the UK. I was on the Isle of Wight, where tourist ads promised 'a sun-filled holiday', but the winters were very dismal indeed.

When the sun shone briefly after many cloudy, dark days, drivers would pull off the highway and get out of their cars to catch the rays, some even shedding their shirts.

Despite the health warnings advising us sunbaking is bad for us, our bodies actually need light in moderation to help us stay healthy. Here are a few ways to help improve your mood and boost your health with light.

• Increase your alertness
  By opening the curtains first thing in the morning.

It will help you wake up and wash off any sleepiness. By taking in the first rays of morning light it will help you blow away the sleepy-time hormone. The retina transfers energy to the brain and sets your daytime clock on the march.

Then as the day fades, consider reducing the amount of light you're exposed to. Turn bright lights off and use lamps instead. This will help with the natural onset of sleep.

• Improve your mood
  By going for a walk around the block in the middle of the day.

The after-lunch energy slump is the natural ebb and flow of your brain waves, and the reason some cultures take a siesta. To fend it off, try walking around the block. Natural light and exercise stimulates serotonin, the mood-regulating hormone, to help re-energise you.

'Another useful time for walking is first thing in the morning,' says Dr Bartlett of the Woolcock Institute of Medical Research. 'It exposes you to early morning light and you get some exercise. And all exercise is good for mood and sleep.'

• Boost your concentration
  By sitting near a window during the day.

Find a sunny, glare-free spot in your place of work to sit - you'll find that the sunlight stimulates your concentration. A California Energy Commission study found performance levels were improved if participants had access to natural light and/or a pleasant view. It will also help you feel good!

• Reduce your risk of illness
  By getting adequate vitamin D - 15 minutes of sunlight a day.

Experts are calling vitamin D the 'darling of the vitamins' and we get it by exposure to sunlight.

Vitamin D is vital to good health. It may reduce blood pressure, protect against breast, bowel and prostate cancer and, in combination with calcium, makes our bones stronger. Even in Australia many people, especially the elderly, and those who culturally cover their skin, have low levels of vitamin D.

For good health we need about 1000 International Units (IU) a day. That's 15 minutes of sunshine, three times a week to produce about 4000 IU. That's as much as you'll get from 40 glasses of milk a day! But many experts also recommend a supplement containing 1000 IU.

For more great tips from Dr John, check out the latest issue of New Idea - on sale now!