You may have a few question marks hanging over your retirement plan, like whether the aging Social Security system will be shored up in time for your farewell party at the office. Even if retirement remains decades away, you've been warned not to rely on Uncle Sam.

While Social Security hogs all the headlines, that's not the problem that should keep you awake at night. Worry about Medicare. It's in much bigger trouble, and that raises serious questions about how future retirees will pay for health care.

It's estimated that Social Security will exhaust its reserves in 2041, but Medicare's hospital insurance trust fund is targeted to deplete its reserves by 2019. In bureaucratic terms, that's just around the corner. With the inflation rate for health care running faster than a sprinter on a triple-shot espresso, the Medicare programs that pay for doctor bills, outpatient services, and prescription drugs have been requiring huge -- and probably unsustainable -- infusions of cash.

Your retirement health
You've probably noticed that you're shouldering more of your health-care costs. I'll bet your health insurance premiums take a bigger bite out of your paycheck, and your out-of-pocket costs may be creeping up, too.

Don't expect this trend to stop when you hit your golden years. In one measure of how escalating health-care costs might pinch your retirement plans, the Center for Retirement Research at Boston College calculated that 44% of households are at risk for not being able to maintain their current lifestyle in retirement. That assumes workers keep punching their keyboards until age 65 and tap into all their financial assets (including home equity) in retirement.

The number of people who will see their standard of living slip in retirement jumped to 61% when the researchers incorporated health-care costs into their equation. That's before any changes to make the Medicare system more sustainable. Who knows whether those changes will tap retirees for bigger contributions?

The good news
That sounds pretty dire. But Fools, like scouts, will always be prepared. If you're not retired yet, you have time to pad your retirement savings to cover the unknowable costs of keeping yourself fit and spry into old age.

Imagine for a moment that you stashed away just a little bit of money during some of your prime earning years, from age 35 to 45. An extra $100 saved each month during that decade can turn into $16,470, even if you earn only 6% on your money.

Let's say you never add an extra dime to that tidy sum, and you just let the money sit around for another 20 years until you wave goodbye to your cubicle forever. You'd have more than $54,000 extra for medical expenses. (Let's hope that copayments don't clock in at $1,000 per visit by the time you get to retirement.)

Better news
That's an improvement, but I'll bet you could do a little bit better. The unknowable cost of health care is yet another reason why anyone with some time before retirement should consider the possibility of better preparing themselves by investing in stocks.

Maybe health-care stocks could be your ticket to a healthy retirement. The most popular names in health care in our Motley Fool CAPS community include Coventry Health Care (NYSE: CVH), UnitedHealth Group (NYSE: UNH), and inVentiv Health (Nasdaq: VTIV).

If you'd rather not pick and choose, you can buy a whole swath of the health-care industry with exchange-traded funds. With a share of the Vanguard Health Care ETF (AMEX: VHT), for example, you can buy into 276 health-care stocks that cover biotechnology, health-care equipment, and pharmaceuticals.

To make sure you're on track for a healthy retirement, learn why:

Start making plans for a better future with the Fool's Rule Your Retirement newsletter. Our retirement doctors can help you diagnose your likelihood for a happy and healthy retirement, and give you a dose of the right medicine to help you get on track. Better yet, it's free for 30 days.

Fool contributor Mary Dalrymple has her doubts about Social Security, Medicare, and Area 51. She does not own any stock mentioned in this article, and she welcomes your feedback. Coventry Health Care and UnitedHealth Group are Motley Fool Stock Advisor recommendations. inVentiv Health is a Motley Fool Hidden Gems pick. The Motley Fool has a robust disclosure policy.