As we grow older, our white blood cells (the soldiers in our immune-system army) decrease in number. A recent study looked at various types of immune cells in adults over time and found that women’s counts fell at a slower rate than men’s did—which might help explain why women tend to live longer. No matter what your gender or age, take care of your immune system: Wash your hands regularly, get plenty of sleep and load up on vitamins C and D.

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