Scientists had 38 women sleep for (a) their usual 7 to 9 hours a night or (b) 1½ hours less (about 6 hours) for 6 weeks each. (The women had excess weight or a family history of type 2 diabetes, heart disease, high LDL cholesterol, or high triglycerides.)

Insulin resistance and fasting insulin levels were higher—signs that the body’s insulin was less effective—when the women got 1½ hours less sleep.

What to do

Aim for 7 to 9 hours of sleep a night, as experts recommend.