Getting too much ― or too little ― sleep can lead to Alzheimer’s disease. A new study published in the journal JAMA Neurology examined the role of sleep in the accumulation of brain amyloid plaque buildup, cognitive performance, and other factors involved in brain aging.

According to Good Morning America, sleeping less than six hours nightly or more than nine hours has a negative effect on health.

“There appears to be a real sweet spot,” said Dr. Jennifer Ashton, the chief medical correspondent for ABC News. “People who got less that six hours sleep on PET scan brain imaging had a higher rate of these brain plaques that we’ve found in association with Alzheimer’s disease.” Ashton added that too much sleep also had negative consequences on cognitive performance.

The researchers discovered that the ideal amount of sleep for healthy aging and brain function is seven to eight hours, according to GMA. They analyzed data from more than 4,000 adults in the U.S., Canada, Australia, and Japan to arrive at their conclusions.

Ashton noted that poor sleep affects the immune system as well, and has been associated with other conditions like increased risk for heart attack, obesity, stroke, and depression.

Sleeping too much also has negative consequences. A study published in the journal Neurology reports that people who consistently sleep more than 9 hours a night, take naps that are longer than an hour and a half, or who get poor quality sleep, have a higher risk of suffering a stroke.

Oversleeping, a condition called hypersomnia, is also linked to mental health issues such as depression, heart disease, metabolic disorders, diabetes and obesity, according to Psychology Today.

Ashton suggests the following tips to improve sleep hygiene and reduce the risk of Alzheimer’s disease and other disorders:

1. Follow a consistent sleep schedule. Try to go to sleep and wake up at the same time daily. You can’t bank sleep, however, and make up for lost slumber on the weekend.
2. Avoid heavy meals, alcohol, and caffeine before bedtime. According to WebMD, foods that contain tryptophan such as milk, nuts and seeds, bananas and honey can help induce sleep. Heavy, fatty foods disrupt digestion and sleep cycles,
3. Keep your environment serene. Remove all electronics and light sources from the bedroom and keep the temperature cool. The ideal temperature for sleeping is between 66 degrees Fahrenheit and 70 degrees Fahrenheit, says Sleep.org.
4. Meditate and exercise during the day. These activities have been shown to induce restful sleep at night.