Nearly 10 million adult children over the age of 50 care for their aging parents, at an average cost of $324,044 in lost wages and Social Security benefits for women and $283,716 for men, according to a new study from MetLife, the National Alliance for Caregiving and New York Medical College.

These extra costs for caregiving are especially troubling because they come just when boomers need to be saving for their own old age.

The study analyzed 2008 government data from a survey of 1,112 Americans over the age of 50 with a living parent. Most were working. About a quarter of the respondents said they had helped a parent financially, giving at least $500 during the previous two years. A quarter of working daughters provided basic care such as dressing, feeding and bathing one or both of their parents. A growing portion, 14%, of working 50-plus sons also provided such care, more often for their fathers.

The MetLife study found that these working caregivers are more likely than other people to say that their health is only “fair” or “poor.”

Women lose more than men in earnings and benefits, according to the study, because they are more likely to drop out of the workplace for a number of years or reduce their hours to care for their parents. Other data found that working caregivers miss out on opportunities for promotions, business travel, education and better-paying jobs that require relocation because they've taken on the responsibility of caring for their family.

A 2009 survey by the National Alliance for Caregiving and the American Association for Retired Persons found that 66% of people giving care arrived late to work, left early or took time during the day to tend others. This survey included those caring for children, but they are only a portion of American caregivers.

More Americans now take care of their mother than a child. Among all caregivers, 26% tend to their mothers and 10% their fathers, compared to 14% who care for a child.

In addition, the MetLife study does not account for the many Americans younger than 50 years of age who are taking care of an adult. The 2009 survey estimates that there are 43.5 million Americans caring for someone age 50 or older.