Which option reflects a physiological change as one ages?

As individuals age, one of the recognized physiological changes is decreased bone density. This decrease can lead to an increased risk of fractures and conditions like osteoporosis. Bone density tends to decline due to a combination of factors, including hormonal changes (such as reduced estrogen in women post-menopause) and a decrease in physical activity levels that typically occurs with aging.

In contrast, reduced body fat percentage typically does not happen universally with age; many older adults may experience an increase in body fat percentage instead. Similarly, improved metabolic rates are generally not observed as people get older; metabolism tends to slow down. Lastly, lung capacity may decline as well, primarily due to structural changes in the lungs and respiratory muscles, rather than being enhanced. Thus, the recognition of decreased bone density as a physiological change in aging is well-supported by studies and clinical observations.