Men in their 30s have the most unhealthy lifestyles since they are the most obese, smoke the most and take the least exercise.
According to the 2012 data released by the National Health Insurance Service on Wednesday, 41.1 percent men in their 30s are obese, 52.8 percent smoke and only 5.7 percent engaged in physical activity at least 30 minutes a day.
The overall obesity rate of men is 38.1 percent and the smoking rate 42.2 percent, with 8.4 percent saying they exercise at least half an hour a day.
Among women, those under 20 smoke the most with 6.3 percent, while the obesity rate is highest among those in their 70s with 39.1 percent. The overall average obesity rate for women is 25.9 percent and the smoking rate 3.3 percent.
The study was based on analysis of over 11 million people who had medical checkups provided by the national health insurance in 2012.
Park Jong-heon at the NHIS said, "Obesity is especially pronounced among men in their 30s, and they smoke a lot due to stress from their work, have trouble finding the spare time to exercise and eat a lot of meat and drink lots of alcohol."
"Because serious symptoms do not tend to show in the 30s, they're actually more unhealthy than men in their 40s, who start to worry about their health."