It's that time of year again when our spirits begin to droop as the days get shorter and darker. Our soggy, sunlight-starved summer is likely to swell the numbers, estimated at half a million people in the UK, who suffer from seasonal affective disorder (SAD).

It's believed that low light levels are responsible for leaving SAD sufferers feeling depressed, fatigued and sometimes craving carbohydrates and sweet foods from late autumn until early spring.

Get a natural high

Exercise is often one of the first things to fall by the wayside when the winter blues strike, but can go a long way towards boosting your mood in the short and medium term.

Lighten up - your guide to beating SAD

BACKGROUND

• Depression and seasonal affective disorder

• Can a spa treatment cure depression?

• Feeling down? Take a dose of Nature's Prozac

• Lighten up winter blues

As anyone who works out regularly knows, being active gives you a natural high through a combination of adrenalin, endorphins and oxygen being released in greater quantities in your body. Add in the neurotransmitter serotonin, which is generated in increased amounts through exercise, and you have a natural chemical pick-me-up. Exercise also keeps your immunity levels high, so you are also less likely to succumb to colds, coughs and bugs.

It's important at the outset to keep your self-image high. Put simply, when you feel out of shape, you tend to do things that do more harm than good, such as eating calorific comfort food and avoiding exercise.

Here are some tips to stop you feeling SAD:

Make the most of daylight hours

With mornings and evenings getting darker, focus on working out at lunchtime or at any other spare time you have during the day. You don't always have to sweat it out for 60 minutes; even just 30 minutes at a lower intensity, preferably outdoors, can be fantastic.

Exercise regularly

Don't be too hard on yourself. Regular readers will know that I advocate building core fitness during winter in readiness for spring and summer, so don't put yourself under pressure to be in the best possible shape now. Aim to be active four times each week, doing at least two workouts at a high intensity, and the other two at a more leisurely pace.

A walk in the park for 30-40 minutes, for example, could replace your usual 20-30 minute run. Adjust your expectations and do the best you can.

Work out together

You don't have to exercise alone. There is plenty of evidence to show that if you do a team sport, exercise in a group (eg, circuit training session) or with a friend, you will stay much more motivated and exercise at a higher level. Knowing that others are relying on you is often just the spur you need to stop slipping into inactivity. It's also much more fun than slogging it out on the treadmill alone.

Do weight training once a week

High-intensity weight training produces a life-affirming shot of adrenalin, testosterone and serotonin. The immediate impact on your shape also ensures that your self-image stays as high as possible, which keeps the blues at bay.

Try something new

Lift your spirits by trying something new that you can do indoors when exercising alfresco isn't an option. You'll find a wealth of exercise DVDs in the shops or at your local library, enabling you to experiment at home. Invite a friend to join you and make a social occasion of it.

Check out your local health club or sports centre. Many offer workouts such as climbing, martial arts and numerous variations on dance and yoga for those who are not keen on the gym.

Most courses run for four to six weeks, so you could try three to four new activities during the winter months, leaving you looking forward to spring with renewed optimism.

For more about Matt, visit www.mattroberts.co.uk

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