Study: You should get 7 hours of sleep each night, not 8

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last updated 8 January 2015

We've all heard that healthy adults should get eight to nine hours of sleep each night to prevent obesity and retain cognitive functions. But an array of new studies suggests those figures might be an hour or two off.

A 2013 poll by the National Sleep Foundation found that people needed seven hours and 13 minutes of sleep to be at their best. (However, 69 percent of people reported getting less sleep than they claimed to need, so take it with a grain of salt.) Other recent studies have found that shooting for around 7 hours of sleep a night might be the healthiest goal — and that going too far under or over that amount can actually contribute to health risks, including diabetes and cardiovascular disease.

A recent study at the University of California San Diego, for example, tracked the sleep habits of 1.1 million people over six years. They found that people who slept between 6.5 and 7.4 hours a night had lower mortality rates than those with less — or more — sleep. Another study, published in the journal Frontiers in Human Neuroscience, found that after seven hours, "increasing sleep was not any more beneficial," Murali Doraiswamy, co-author of the study, told The Wall Street Journal.