Next time you consider choosing the TV over a run, think carefully. A staggering one in three women and one in four men do not do enough physical activity, a study by the World Health Organisation (WHO) has found.

This inactivity is putting them at risk of heart disease, type 2 diabetes, dementia, and some cancers.

In 2016, more than a quarter (1.4 billion) of the world’s adult population didn’t exercise enough, research showed. WHO added that since 2001, there has been little progress in improving people’s activity levels.

“Unlike other major global health risks, levels of insufficient physical activity are not falling worldwide, on average, and over a quarter of all adults are not reaching the recommended levels of physical activity for good health,” warned the WHO’s Dr Regina Guthold.

People are advised to do at least 150 minutes of moderate-intensity exercise per week, or 75 minutes of high-intensity physical activity.

Dr Luke Powles, GP for Bupa UK, tells HuffPost UK that staying active is important as it helps us to maintain a healthy weight and blood pressure, which in turn keeps our heart healthy. But how else does it help us?

If you don’t exercise, you could become overweight which can put the heart under increased pressure, says Dr Powles. This can lead to a higher risk of heart disease, heart attack and type 2 diabetes.

Being overweight can also lead to increased pressure on our joints – like our knees – making it harder to get back into exercise. “Carrying more weight than our skeletons were designed for puts increased load on weight-bearing joints which can accelerate wear and tear changes, increasing the risk of arthritis,” he explains.

Exercise is also linked to higher levels of HDL cholesterol, or ‘good cholesterol’, which has been found to protect against heart disease.

Physical inactivity can also negatively impact our muscles and bones, says Mike Primett, physiotherapist for Bupa Clinics. This is because muscles respond to the demands we put on them and so the more we use them the stronger they should be. “If you don’t exercise your muscles won’t be as strong,” he explains. “And it’s not just our muscles that get weaker – a lack of exercise can impact our bones too.

“Keeping active helps us maintain healthy calcium levels and bone density, preventing brittle bones. What’s more, exercise is proven to help prevent trips and falls. As such, people who avoid exercise are likely to have weaker bones, along with more exposure to situations where fractures can occur.”

It’s no secret exercise has mental health benefits too. Physical activity releases endorphins and serotonin which are natural ‘feel good’ chemicals, helping elevate our mood. “These are obviously positive for people taking up exercise but, on the flip side, people who stop exercising regularly might find their mood drops as a result,” Dr Powles says.

“What’s more, exercise can be a good coping mechanism for people facing high levels of stress or anxiety. This is because it can help divert our focus on to something positive, allowing us to keep a clear head and combat stress.”

Studies have found that people who exercise more will sleep better and feel more energetic, so if you stop all of a sudden it could make you feel even more tired and lethargic, and you may not sleep as well as you once did.

People who don’t exercise at all might also find their immune system suffers. This is because moderate exercise can help keep down levels of the stress hormone cortisol. 

“If this is kept elevated for longer periods of time, it can reduce the immune system’s ability to fend off bugs and illnesses,” Dr Powles adds. “Regular exercise has also been shown to help reduce the risk of some cancers.”