According to the National Sleep Foundation, adults need seven to nine hours of sleep to function well the next day. Here's why:
1. Your brain: Too little sleep can slow memory, learning and cognitive abilities, including critical thinking, math skills and spatial orientation. It can also trigger irritability and is often associated with depression. And it can change the brain’s sensitivity to neurotransmitters, increasing vulnerability to mood disorders.
2. Your heart: Women who sleep five hours or less per night tend to have higher markers of systemic inflammation than those who regularly get seven hours, according to research from the United Kingdom. Also, a study at Columbia University in New York City suggests that too little sleep increases your risk of developing hypertension over a 10-year period.
3. Your weight: Not getting enough rest can change levels of hormones that regulate appetite and satiety, which can make you prone to adding pounds. Women who slept less than five hours a night had a higher rate of weight gain over 16 years than those who got seven hours, according to a study at Case Western Reserve University in Cleveland.
4. Your immune system: Skimping on shut-eye can hurt your ability to fight off colds, flu and other infections—and affect your response to vaccinations. Research in Germany found that people who had a full night’s rest after getting the hepatitis A vaccine released more immune-boosting hormones those who were sleep deprived after the shot.
5. Your hormones: Erratic sleep patterns can cause unusual fluctuations in levels of cortisol (a stress hormone), according to a study at Dalhousie University in Halifax, Nova Scotia. And research at Columbia University found that regularly hitting the hay five or fewer hours per night is linked to insulin resistance and an increased risk of type 2 diabetes.