Immune System

Age-related changes in the immune (lymphatic) system increase vulnerability to infections, tumors and immune disease. Factors that affect immune system function include hormonal changes, age, nutrition, and psychological factors (e.g., stress). As we grow older, our bodies are less able to produce antibodies which are important in fighting infections. As a result older adults are at greater risk for infections and the mortality rate from infection is much higher than in the young. Older adults are 3 times more likely to die of pneumonia or sepsis, 5 to 10 times more likely to die of urinary tract infections, and 15 to 20 times more likely to die of appendicitis.

The thymus gland produces hormones that are important for the development of white blood cells. White blood cells are the "phages" of the immune system-- they attack and isolate foreign materials. The involution (shrinking) of the thymus gland begins after adolescence and the level of thymic hormones decreases by age 30. By age 60 thymic hormones cannot be detected in the blood.

As we age, the immune system also responds less vigorously to skin tests in which a foreign substance is injected below the skin surface, indicating a diminished response to antigens.