Stress appears to weaken and age your immune system. In a new study published in the Proceedings of the National Academy of Sciences, researchers at the University of Southern California analyzed questionnaire responses from over 5,700 adults over the age of 50. Participants discussed their lifestyle and professional stresses, traumatic events and discrimination. The researchers then analyzed blood samples from the participants. People with higher stress scores proved to have older, weaker immune systems, with lower percentages of healthy disease-fighting immune cells. The researchers also found that people who experience more stress tend to have worse diet and exercise habits, which might partially explain the immune system aging. Lowering stress, exercising on a regular basis, and eating a diet of healthy foods appears to boost your immune system and lower your risk of cancer, cardiovascular disease and infections.