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.