Doing more housework keeps stress levels higher at the end of the day for both married women and men, increasing health risk, U.S. researchers suggest. Researchers Darby Saxbe, Rena Graesch of the University of California, Los Angeles, and colleagues tracked 30 dual-earner couples around their homes for three days, using video cameras, interviews and surveys. They required the study participants to provide four saliva samples every day to measure the stress hormone cortisol, which is usually high in the morning -- and during stressful situations -- and tends to recover later in the day. Saxbe says a steeper drop in the hormone is considered healthy. Cortisol levels can affect sleep, weight gain, burnout and weakened immune resistance. On average, wives spent more of their time at home doing housework, followed by communication and leisure, while husbands had more leisure time, followed by communication and housework. The study, published in the Journal of Family Psychology, found both wives and husbands who devoted more time to housework had higher levels of evening cortisol and weaker afternoon-to-evening recovery. However, husbands who apportioned more time to leisure, and whose wives apportioned less time to leisure, showed stronger after-work recovery, the study says. The findings suggest how the division of labor within couples is structured can implicate health, the researchers say.