Why your child's bedtime (and breakfast!) matter when it comes to weight.

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boy looking for midnight snack in the fridge
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You probably already know that genetics play a big part in your child's weight. But does it surprise you that your child's bedtime may affect her chances of becoming overweight or obese? In a recent study, researchers tracked the heights and weights of more than 16,000 kids in the UK at ages 3, 5, 7, and 11. The majority of the kids remained in a healthy BMI (Body Mass Index) range. But among the children whose BMIs were more likely to climb into the overweight or obese categories, researchers uncovered these three surprising risk factors:

1. Maternal Smoking

Though smoking often leads to low birth weight, it may have the opposite effect long-term. Though the reasons aren't fully understood, it may be that after a baby experiences nicotine withdrawal at birth, the appetite (and weight gain) surge. "We know that babies who gain weight rapidly in the first year of life are at notably increased risk for long-term problems with weight," says Natalie Digate Muth, M.D., a member of the American Academy of Pediatrics' Committee on Nutrition. Babies born to moms who smoke may also have decreased motor skill development that can lead to low activity and higher weight, she adds.

2. Irregular Bedtimes

Here's another reason to stick to a stable bedtime routine: Kids whose bedtimes were irregular were also more likely to have higher BMIs. "It doesn't surprise me that irregular routines like late or inconsistent bedtimes are associated with increased BMI because I see it play out in real life with many of my patients," says Dr. Muth. One reason: Kids who are staying up late are more likely to snack after dinner, sometimes on high-calorie foods. Other research has also found that sleep deprivation can boost appetite by affecting hormones that regulate hunger.

3. Skipping Breakfast

This may seem counterintuitive since skipping a meal should mean fewer overall calories. But skipping breakfast can lead to a major boost in appetite later in the day, which could cause kids to ultimately overeat, says Muth.

But there's hope—because these risk factors have something else in common: They all have the potential to be changed, note the researchers. And they provide powerful motivation in their study: The children whose BMIs rose into the overweight and obese categories were also more likely to report emotional problems like unhappiness, poor self-esteem, and body dissatisfaction.

Sally Kuzemchak, MS, RD, is a registered dietitian, educator, and mom of two who blogs at Real Mom Nutrition. She is the author of The Snacktivist's Handbook: How to Change the Junk Food Snack Culture at School, in Sports, and at Camp—and Raise Healthier Snackers at Home. She also collaborated with Cooking Light on Dinnertime Survival Guide, a cookbook for busy families. You can follow her on Facebook, Twitter, Pinterest, and Instagram. In her spare time, she loads and unloads the dishwasher. Then loads it again.