Answer to Question 1
The BMR begins to decrease in early adulthood (after growth and development cease) at a rate of about 2 percent/ decade. A reduction in voluntary activity as well brings the total decline in energy expenditure to about 5 percent/decade.
Answer to Question 2
Age: Lean body mass diminishes with age, slowing the BMR.
Height: In tall, thin people, the BMR is higher.
Growth: In children, adolescents, and pregnant women, the BMR is higher.
Body composition (gender): The more lean tissue, the higher the BMR (which is why males usually have a higher BMR than females). The more fat tissue, the lower the BMR.
Fever: Fever raises the BMR.
Stresses: Stresses (including many diseases and certain drugs) raise the BMR.
Environmental temperature: Both heat and cold raise the BMR.
Fasting/starvation: Fasting/starvation lowers the BMR.
Malnutrition: Malnutrition lowers the BMR.
Hormones (gender): The thyroid hormone thyroxine, for example, can speed up or slow down the BMR. Premenstrual hormones slightly raise the BMR.
Smoking: Nicotine increases energy expenditure.
Caffeine: Caffeine increases energy expenditure.
Sleep: BMR is lowest when sleeping.
The effects of aging can be seen in the decline in function of many physiological systems.
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