Adults generally need between 7 and 9 hours of sleep per night for optimal health and functioning

. Sleeping less than 7 hours regularly has been linked to various health problems, including increased risk of diabetes, depression, and impaired immune function

. Older adults (65 years and older) are typically recommended to get slightly less, about 7 to 8 hours per night

. Sleep quality also matters, with about 1.5 to 2 hours of deep sleep being important for physical restoration and overall wellbeing

. The exact amount of sleep needed can vary by individual due to genetics and lifestyle, but consistently getting less than 7 hours is generally detrimental

. In summary:

• Recommended sleep for adults (18-64 years): 7 to 9 hours per night
• Recommended sleep for older adults (65+ years): 7 to 8 hours per night
• Less than 7 hours regularly is associated with negative health outcomes
• Deep sleep (about 1.5-2 hours) is essential for bodily repair and health

These guidelines reflect consensus from major health organizations and research institutions.