This daily health update discusses several recent studies on various health topics: 1) A study found that women have more difficulty recovering from heart attacks than men, possibly due to higher stress levels. 2) Exposure to mercury, even at low levels, may increase risk of autoimmune diseases in women by affecting antibody levels. 3) A study linked low vitamin D levels in childhood to increased risk of heart disease as an adult. 4) Brief naps can help counter the negative health effects of poor sleep by helping the body recover physiologically.