Not only does exercise improve your health, even if you have already been diagnosed with something, but it can go a long way to prevent the onset of several life-threatening conditions, such as heart disease, diabetes and cancer.

And exercise can make you look great – younger, fitter and thinner. Who needs any more convincing?

We have scrutinized the medical journals. Here's a summary of the proven health benefits of exercise:

1. It is good for your heart
"Even a moderate amount of exercise helps your heart," says Dr William Kraus, associate professor of medicine at Duke University Medical Centre in an article published in The New England Journal of Medicine. "Some exercise is better than none and more is better than less."

Exercise reduces LDL cholesterol, the kind that clogs arteries. It also reduces your blood pressure, relieving stress on your heart; improves your insulin sensitivity; improves heart muscle function and blood flow and diminishes the chances of developing blood clots. These findings have been corroborated by a host of studies over the years.

2. Exercise promotes weight loss
Research has shown that to have an effect on weight loss you need to exercise for at least 30 minutes a day. You can also do an hour of intensive exercise every second day if this fits into your schedule more easily. Be consistent and be regular. Do those one-hour exercise sessions three to four times every week, not just one week a month, and you will achieve the result you desire - to lose weight and keep it off, says Dr Ingrid van Heerden, registered dietician.

3. Exercise prevents osteoporosis
Exercise, together with a healthy calcium intake, builds strong bones. Weight-bearing exercises, like running, walking and weight-lifting, help lower your odds of getting osteoporosis as you grow older, according to experts.

Ideally, you should start when you're young, but it's never too late to pick up the habit. Even a brisk walk can help, say metabolic disease specialists.

4. Exercise lowers high blood pressure
Exercise is good for your blood pressure - no matter your age, weight, race or gender. And it really doesn't matter whether you get exercise from a brisk walk, a fast run or a few laps in the pool; the results are equally good.

The studies on which these findings were based used "aerobic" exercise - activities that increase heart rate and improve the body's ability to use oxygen. Most of the studies involved participating in one or more aerobic activity for 20 - 30 minutes per session, several times a week.

On average, exercise helped study participants reduce systolic (top number) pressure by nearly 4 mm Hg, and diastolic (bottom number) pressure by slightly more than 2.5 mm Hg. But experts caution that those with extremely high blood pressure should not rely on exercise alone to control hypertension.

5. Exercise is an excellent de-stressor
It is general knowledge: exercise counters stress and depression. But exactly how and why does this work?

Exercise acts as a temporary diversion to daily stresses and it improves self-esteem. Increased core temperature during exercise may lead to reduced muscle tension and favorable alterations in brain neurotransmitters. Mood improvements may also occur due to the increased secretion of endogenous (internal) opiates, e.g. endorphins. Psychological changes may occur because of changes in nor epinephrine, dopamine and serotonin, all hormones which can affect mood and anxiety levels.

6. Exercise prevents colds
One doesn't automatically associate regular exercise with a reduction in the number of colds people get. But researchers from the University of Carolina found that people who exercised regularly were 23% less likely to get colds than those who exercised less. And if those who exercised got colds, the symptoms disappeared more quickly than in the study participants who did little exercise.

Health experts believe that exercise spikes the immune system for a few hours each day, helping to ward off colds. Thirty minutes of brisk walking is enough to make you reap the benefits of exercise.

7. Exercise reduces the severity of asthma
Many people who suffer from exercise-induced asthma, understandably try to avoid exercise.

But sports medicine specialists say it's possible for asthmatics to continue exercising if they use preventive medications wisely and avoid certain triggers that exacerbate attacks. Exercise-induced asthma can be made worse by cold, dry air or air containing high levels of pollen or pollutants. The extra effort made to stay fit pays off in fewer or milder asthma attacks overall and a need for less medication.

Experts recommend swimming as one of the best exercises for people with asthma.

8. Exercise reduces diabetic complications
Lifestyle factors have a huge impact on certain conditions – and diabetes is one of them. Exercise can help to reduce your insulin requirements, lower your cholesterol levels and high blood pressure, and in the long term can reduce the development of heart disease and stroke. This is important because diabetics have a higher risk of developing heart and circulatory problems. Exercise can also promote weight loss, improve circulation and reduce stress levels (raising your glucose level).

9. Exercise promotes a healthy pregnancy
Although exercise might be risky in some cases, the benefits of exercising during pregnancy generally far outweigh the risks and some women can even exercise up until the third trimester. Relaxation exercises, Kegel exercise that strengthen the pelvic muscles and back exercises are all important for pregnant women.

10. Exercise plays a role in preventing cancer
At least 35% of all cancer deaths may be related to overweight and lack of activity, a recent study from the Seattle Cancer Research Centre has found. Exercise is believed to speed the passage of food through the colon, thereby reducing the amount of time that any toxins are in contact with the body. Overweight people also tend to have more insulin, which promotes the growth of tumors. For women, exercise reduces the level of estrogen, a hormone linked to breast cancer.

11. Exercise has anti-ageing effects
Exercise enhances blood flow to the brain, possibly reducing risk of stroke. It also improves reasoning and memory.

Regular exercise arouses the brain and slows down degeneration of the central nervous system, which leads to slower reaction times and poorer coordination.

Exercise also increases strength and size of muscles and improves lung function. Regular exercise can reduce body fat and lower the risk of chronic lifestyle diseases in the elderly. Recent literature suggests that the greatest threat to health is not the aging process itself, but rather inactivity.

12. Exercise promotes brain health
If you thought exercising your brain meant only doing a few crossword puzzles or learning a language, you may be wrong – rather put on your walking shoes and get moving. This was the finding of researchers from the University of Illinois.

Their study found that the brain responses in active seniors were comparable to those of young adults.

It is thought that exercise increases the flow of blood to the brain, just as it improves circulation to the heart and the rest of the body. Activity also stimulates the growth of nerve cells in the part of the brain involved in memory.

13. Exercise is great for your sex life.
The medical research points towards it: the fitter you are, the better your sex life is.

The reason seems to be two-fold: psychologically you feel better about yourself and more inclined towards sex, and physically, being fit improves libido, blood circulation and sexual functioning.

It has been said before that the brain may be the most important sexual organ. This is because stressed, anxious and depressed people are usually unable to enjoy a healthy sex life. Additionally, people with a bad body image do not feel good about their bodies and often avoid sex or are unable to truly enjoy it.

According to the American Council on Exercise (ACE), being physically active can be “a natural Viagra boost”. “Men and women who exercise regularly are going to have increased levels of desire. They’re going to have enhanced confidence, enhanced ability to achieve orgasm and greater sexual satisfaction,” says Cedric Bryant, the council’s chief exercise physiologist.

14. Exercise improves sleeping patterns
Relaxation exercises will help you to ease tension and relieve headaches, backaches and insomnia. Exercise releases the body's own painkillers, called endorphins, into your system. It also helps you to gain a sense of emotional wellbeing and a feeling of being more in control.

Exercise during the day promotes the onset and quality of sleep, according to the South African Memory Resource Centre. But you need to exercise at the right time: the ideal time for exercise is in the morning. Exercising late in the day can contribute to sleeplessness, because exercise causes an increase in your body's energy.

15. Exercise combats impotence
If you stop and think about it, it makes sense - increased circulation as a result of exercise should result in lower levels of impotence, as getting an erection is dependent on the efficiency of blood circulating to the penis.

"Losing weight, stopping smoking and doing more exercise are associated with better sexual health," says Dr Andrew McCullough, director of Male Sexual Health, Fertility and Microsurgery at New York University Medical Center in New York City. "We talk so much about treating, treating, treating. Here we're beginning to see an increasing body of evidence that we can modify the appearance of this by changing lifestyle."

16. Exercise helps prevent stroke
Need another reason to make good on that long overdue promise to get more exercise? It can dramatically cut your risk of stroke.

"Highly active" people had a 27 percent lower risk of having a stroke or dying if they had one, compared with sedentary folks. And people who were "moderately active" had a 20 percent lower risk.

These findings are based on a review of 23 international studies that appear in the October issue of the journal Stroke, the Associated Press reports.

Jogging 15 to 20 minutes a day most days would qualify as highly active. Brisk walks of 30 minutes a day on most days would qualify as moderate activity, the AP says.

17. Exercise is good for mind and soul.
In a synopsis on “Exercise, Fitness and Mental Health” (1990), sports psychologist D.R. Brown summarized the possible beneficial effects that exercise has on mental health. These include the following:

• Exercise may act as a temporary diversion to daily stresses.
• Exercise provides an opportunity for social interaction that may otherwise be lacking in an individual’s life.
• Exercise provides an opportunity for self-mastery. Increasing fitness or improving body composition and other health parameters may improve an individual’s self-esteem.
• Increased core temperature during exercise may lead to reduced muscle tension or alterations to brain neurotransmitters.
• Mood improvements may occur due to the increased secretion of endogenous (internal) opiates e.g. endorphins
• Psychological changes may occur due to alterations in nor epinephrine, dopamine and serotonin, all hormones which can affect mood and anxiety level.

18. Exercise improves oxygen and nutrient supply to all cells in your body.
An American study indicates that ‘80-plus-ers’ can dramatically improve their health by exercising a few times a week. If this is true for elderly people, it certainly is for the younger set as well.

Exercise apparently not only improves the body's utilization of oxygen, but also lowers systolic blood pressure (high pressure is a dangerous condition common in elderly people).

Positive results were obtained from the 22 elderly people (80 years and older) who took part in the study at the Veterans Affairs Ann Arbor Healthcare System in Michigan.

19. Exercise allows you to improve muscle strength, joint structure and joint function
Strengthening exercises increase not only muscle strength and mass, but also bone strength, and the body's metabolism.

A certain level of muscle strength is needed to function every day and do things such as walking and climbing stairs. Strengthening exercises increase this muscle strength by putting more strain on a muscle than it is normally accustomed to receiving. This increased load stimulates the growth of proteins inside each muscle cell that allow the muscle as a whole to contract.

Exercise can promote joint health for everyone, but particularly for people who suffer from arthritis. Arthritis is a general term for over 100 different conditions that cause pain, stiffness and often inflammation in one or more joints. Exercise can reduce some arthritis symptoms and improve joint mobility and strength.

Osteoarthritis is the most common form of arthritis. Normally, the two bones of a joint are cushioned with a strong flexible tissue called cartilage. In osteoarthritis, the cartilage deteriorates, causing pain and stiffness.

Cartilage doesn't have a blood supply; it relies on synovial fluid moving in and out of the joint to nourish it and take away waste products. Exercise helps this process.

20. Exercise helps to manage arthritis
Regular, intensive exercise for patients with rheumatoid arthritis builds muscle strength and aerobic capacity, improves the ability to do daily tasks and fosters a sense of emotional well-being.

That's the conclusion of a new study by Dutch researchers who tracked 300 people with rheumatoid arthritis (RA) for two years. About half the patients participated in a one-hour exercise regimen twice weekly; the rest received traditional treatment, including physical therapy, if prescribed by their physicians.

The findings, appearing in the latest issue of Arthritis & Rheumatism, suggest high-intensity exercise programs can benefit many RA patients, says researcher Dr Thea Vlieland of Leiden University Medical Centre.

The positive effects on muscle strength and aerobic capacity could be translated into an improvement in the activities of daily living, and this is what really makes a difference in your life, Vlieland says.