Maybe you’ve heard that to be healthy, you should have “moderation in all things.” Eat, but don’t eat too much; drink, but not to drunkenness; exercise, but not to exhaustion, and so forth. A new study suggests that we even need to use moderation in the way we sleep!

Dr. Kristen G. Hairston of the Wake Forest University School of Medicine just published an article in the journal Sleep showing “a clear association between averaging five hours or less of sleep each night and large increases in visceral fat, or fat around the organs” for people under 40. As we’ve said before, “Visceral fat is a major risk factor for everything from metabolic syndrome to organic brain disease to liver cancer and prostate cancer.”

Nevertheless, lots of extra sleep isn’t good either. The same study found that people who slept more than 8 hours per night also had higher BMI measurements, more subcutaneous fat, and more visceral fat than people who managed to sleep 6-7 hours nightly.

One caution about this study: it only involved Hispanics and African Americans. Why? “Short sleep has become more common in the United States and minorities are disproportionately affected, said Hairston, an affiliate of the Maya Angelou Center for Health Equity, part of the School of Medicine. They are also more prone to metabolic conditions, including increased rates of obesity, insulin resistance and type 2 diabetes.” So it remains to be seen whether the correlation between sleep and fat is also true among other ethnic groups.