A TIAA-CREF survey on retirement savings shows one third of people nearing retirement wish they had invested more aggressively during their lifetime.

Being too conservative in their investments was one of the top regrets for people age 55 to 64 who were in an employer-sponsored retirement plan, according to TIAA-CREF's Ready to Retire survey released Wednesday.

Fifty-two percent of those nearing retirement wish they had started saving sooner, and 47 percent wish they had saved more of their paycheck, the survey says. The survey included 1,000 participants, 140 of whom were between 55- to 64-years-old.

Sixty-eight percent of those approaching retirement say they are unprepared for their future.

“This research reinforces that preparing for retirement shouldn’t become a sprint to the finish, but rather a long-distance pursuit that requires careful planning throughout an adult’s life,” says Teresa Hassara, executive vice president of TIAA-CREF's Institutional Business.

According to the survey, financial challenges make up three of the top four concerns for individuals close to retirement. Many worry about not having enough money to cover their monthly expenses (45 percent), while others are anxious about how health-care costs (35 percent) or inflation (32 percent) could deplete their retirement savings, TIAA-CREF says.

To supplement their savings in retirement, 42 percent of the near retirees say they plan on working part time, 39 percent say they will spend more conservatively, and 23 percent say they will move to less expensive homes, the survey says.