Are you getting fewer than six or seven hours of sleep each night? If so, know that hitting the sack after midnight may increase your risk of heart disease, especially if you’re male, says a recent study that explored the relationship between heart health and bedtime.

Researchers at the Miso Health Clinic in Gifu, Japan, studied 251 healthy men, ages 60 and below, who completed questionnaires about their bedtime habits. The men indicated how much they slept each night and what time they turned in. All participants were given annual checkups measuring their body weight, blood pressure, body mass index (BMI), waistlines and lipid levels.

The results? Men who slept fewer hours had elevated blood pressure levels, higher BMI and hardening of the arteries. While researchers aren’t sure why they got these results, some cited a previous study that suggests those who go to bed late may eat more at night and thus raise their risk of obesity, a risk factor for heart disease.

Learn more about sleep by reading RH’s “Good Night (and Good Luck!)