Bad diets and unhealthy lifestyles have become the biggest threat to life expectancy, fuelling seven in 10 deaths, a major Lancet study has found.

The research on almost 200 countries found that increases in life expectancy – achieved thanks to improvements in sanitation and immunisation – are being eroded by the global obesity crisis.

The Global Burden of Disease study gathered data on 249 causes of death, 315 diseases and injuries and 79 risk factors in 195 countries and territories between 1990 and 2015.

While deaths caused by infectious diseases such as malaria and flu have fallen sharply, the proportion of fatalities fuelled by lifestyles have soared.

In total, 71.3 per cent of deaths last year were caused by non-infectious diseases, the study shows – a rise from 57.6 per cent per cent in 1990.

These include conditions such as heart disease, stroke, cancer and diabetes, all of which are affected by diet and lifestyle.

The research found high blood pressure – which is fuelled by obesity and lack of exercise – was the top risk factor for deaths, contributing to over 9 per cent of global health loss.

This was followed by smoking (6.3 per cent), high blood sugar (6.1 per cent), and high body mass index (5 per cent).

And although UK adults are living longer, millions are finding their later years blighted by poor health, the study found. On average, women can expect to spend their last 10 years in ill-health, the report says, while men will spend their last nine year suffering from health problems.

Professor John Newton, chief knowledge officer at Public Health England said: “Countries used to worry about the impact of infections like HIV, malaria and measles on people’s health, but now it’s the fallout from poor diets, smoking and drinking too much. ”

“On one hand, it’s a sign of successfully preventing infections, but on the other, it tells us how much more we have to do.”

The findings showed that healthy life expectancy had increased steadily in 191 countries, adding an average 6.1 years to people’s life spans over the course of 15 years.

But overall life expectancy had risen further, by 10.1 years, suggesting that by 2015 people were spending a greater proportion of their lives in ill-health.