Even the wealthy worry about health care costs in retirement, a new study says.

Health care is the top threat to financial peace of mind for those with $5 million or more in investable assets, according to a survey by Age Wave, which studies age-related issues, and Merrill Lynch. The survey includes 202 high-net-worth individuals 50 years of age and older with at least $5 million in investable assets.

Similar to the general population, 88 percent of high-net-worth individuals say a health problem is their top impediment to financial peace of mind. High-net-worth individuals are more likely to feel financially prepared for retirement, but 30 percent are still uncertain about having enough money to fund a retirement that lasts 30 years.

Sixty-nine percent say they also worry about a loved one having a costly health issue.

Compared to the general population, affluent Americans are much more likely to say rising tax rates (65 percent versus 27 percent) and a downturn in the stock market (62 percent versus 20 percent) also are among their top financial concerns in retirement.

They are also more likely to cite negative news in the media about the economy as a worrisome factor, with 38 percent of the high-net-worth and 27 percent of the general population saying it is a concern.

Where the roles reverse is concern over inflation. Fifty-one percent of the general population worries about inflation affecting their retirement, while only 20 percent of high-net-worth individuals find it a concern.

Compounding the financial worries, according to the survey sponsors, is that wealthy individuals are even more prone to secrecy about their finances than the general population. Sixty-two percent of high-net-worth people say finances are a private matter even among close family members and friends, compared to 33 percent of the general population.