Production of most hormones declines with age, and even for those that don’t, hormone receptors usually become less sensitive. Notable hormones that decline with age include oestrogen and testosterone (related to a decrease in reproductive health), growth hormone (related to decreased muscle mass and regenerative capacity), and melatonin (related to sleep loss).
The thyroid gland produces less of the thyroid hormones with age, which leads to a gradual decrease in metabolic rate. This leads to less heat production and increased body fat.
Insulin sensitivity declines with age, and insulin levels may decrease, contributing to an increased risk of diabetes.