How often do you complain of feeling run down, knackered and under the weather? If you find yourself feeling generally listless, you need to look closely at diet, sleep, stress and fitness factors and take action immediately, because you may be suffering from: thyroid problems For some, being tired isn't simply a case of trying to do too much.

They may have an underactive or overactive thyroid, which makes them feel permanently drained. It can be hard to diagnose because there are so many symptoms. Your thyroid regulates your metabolism and it needs vitamin C to function properly. But it's not a case of the more, the merrier - too much vitamin C actually inhibits thyroid function.

Action plan?

Trace minerals, like selenium and zinc, are necessary to convert the thyroid hormone into energy. Without these, you'll feel sluggish and have a low metabolism. So eat more bran, onions, kidney beans and mushrooms.

If you've had a major crisis in your life, you may overproduce the hormones cortisol and adrenalin, which makes your thyroid go haywire. But if your tiredness is due to lack of sleep, your pineal gland may not be producing enough melatonin, which signals your brain to rest. Make sure your room is as dark as possible.

Blood sugar imbalances If lack of energy is accompanied by irritability, lack of concentration, the shakes, feeling woolly-headed or have sugar cravings, you could have a blood-sugar imbalance. Irregular eating habits and eating certain kinds of foods release sugar into your blood too quickly, causing large peaks and dips.

Carbohydrate foods have a low GI (Glycaemic Index), which keeps your blood sugar balanced. When a carbohydrate is eaten with protein, the net effect is even more energy sustaining.

Action plan?

Ditch your croissant, sugary cereal and white toast and jam and, shock horror, your morning coffee. Your blood-sugar level gets only a short-term boost, before crashing a few hours later, leaving you exhausted. Oats are the best grain and plums and cherries the best fruit. Brown basmati rice, quinoa, lentils and beans are excellent. Try porridge with berries to start the day.

an iron deficiency According to the recent National Diet and Nutrition survey, 91% of women in the UK don't get enough iron in their diet. Iron is needed for the formation of haemoglobin, which is in red blood cells, and it's the substance that transports oxygen around the body.

Action plan?

Eat more iron-rich foods such as eggs, brown rice and tuna. Tea and coffee contain tannin and phytates, which inhibit iron absorption, so it's better to wait at least 30 minutes after eating before drinking them. Slow cooking reduces the amount of iron remaining in your food, whereas steaming vegetables means more iron is retained.

Stress Stress affects your body in a number of ways, including anxiety, exhaustion, appetite problems, headaches and sleep problems.

It also weakens your immune system, making you susceptible to infections. It has also been blamed for triggering up to 85% of chronic illness, like depression.

Action plan?

Start the day with a cup of hot water and the juice of half a lemon. This balances the acidity caused by stress. Replace refined foods with natural ones, like fruit, for a sweet hit. Natural foods provide energy, refined foods steal energy because they're harder to digest.

Take one step at a time. Stress causes us to speed up, so you have to train yourself to slow down.

Lack of exercise Exercising sends a signal to the pituitary gland in your brain to release endorphins, your feel-good drug. Endorphins are crucial for the release of serotonin, our happy hormones, which promote positive thinking and vitality.

Lethargy and fatigue aren't good emotions, but can be minimised with exercise. Researchers at Leeds University recently found women who work out in the morning reported less tension and greater feelings of contentment.

Action plan?

Exercise in the morning when your metabolism is most sluggish.

Once your metabolism is raised, it stays up for most of the day, which means calories and fat are used at a higher rate.

An out-of-sync body clock Your body has a built-in cycle, called a circadian rhythm, that lasts around 24 hours and automatically affects all your basic bodily functions, including your sleep-wake cycle, alertness, appetite and energy levels. Late nights, international travel and irregular sleep are a recipe for disaster because your internal body clock is so powerful it's senseless fighting against this natural pattern.

Action plan?

Timing of your meals is a vital part of the body-clock approach to fighting fatigue and regular meal times can help reset your body clock. If you often eat for comfort, follow strict diets, eat big portions or skip meals, you override the action of the chemical messengers that regulate your hunger, energy levels and mood. Include slow-releasing energy (low GI) foods, such as pasta, lean meat and nuts in your diet.

Finally, get a good night's sleep, which means about seven to eight hours a night. Studies have found that not getting enough sleep disrupts hormones that regulate your hunger and metabolism, making you more likely to overeat and resulting in peaks and dips in your blood sugar.