Chronic stress that keeps you up at night can increase the production of fat cells.

A good night’s sleep may help prevent weight gain by eliminating middle-of-the-night worry sessions that can cause fat cells to flourish.

That’s what Stanford University School of Medicine researchers concluded after exploring the molecular workings of chronic stress. 

It’s all about when the body releases glucocorticoid hormones — primarily cortisol — which spur fat-cell production. (This may explain why taking glucocorticoid drugs, used to treat asthma and rheumatoid arthritis, is often linked to obesity.)

Researchers exposed precursor fat cells to glucocorticoids in timed pulses and then stained them to determine how many had matured into fat cells. The findings, published in Cell Metabolism, indicate that it’s the time the stress occurs that most ­affects fat-cell development.

Normal levels of glucocorti­coids fluctuate in a circadian 24-hour cycle, peaking around 8 a.m., bottoming out around 3 a.m. the next day, and then spiking again about five hours later. The rise is a wake-up signal that gets us moving and activates our appetites. Glucocorticoid levels in the bloodstream are also boosted by different types of stress.

Chronic exposure to glucocorticoids — more than 48 hours — increased fat-cell production, as did even brief nighttime exposure, such as a midnight anxiety session. Conversely, precursor cells that weren’t exposed to stress hormones for a 12-hour period, as during a peaceful night’s sleep, didn’t turn into fat cells. Daytime stress was not found to contribute to fat gain