As the science of sleep evolves, researchers continue to study how napping may influence a person’s health. Shorter, power naps can boost alertness. Longer naps, especially those lasting an hour or more, have been linked with obesity and increased cardiovascular disease risks. Oftentimes, these findings volley back and forth.

To better understand connections between daytime naps and health, researchers assessed data taken from more than 3,200 adults living in Spain, a country where midday naps, or siestas, are common. They found that about one-third of adults took regular siestas – oftentimes four days a week. Among regular nappers, those who snoozed for 30 minutes or less were 21% less likely to have elevated blood pressure compared to non-nappers. Those who napped for more than 30 minutes were more likely to have a higher body weight. They were also 41% more likely to have high blood pressure, high blood sugar, and a larger waist circumference.

Upon further analysis of the data, the researchers found that certain activities, including going to bed later, smoking, and having larger lunches later in the day, helped explain links between longer naps and increased cardiovascular disease risks. They conclude that more research is needed to distinguish how and when daytime naps could support or improve a person’s cardiovascular health. The research published in Obesity and was partially funded by NHLBI and the National Institute of Diabetes and Digestive and Kidney Diseases.