Despite all the talk about the shaky future of Social Security, its potential shortfall isn't the biggest risk for future retirees. They should be worrying about Medicare instead.

The government's health insurance plan for retirees is on a crash course with the realities of an aging population and an increasingly expensive medical system. It's projected to go bust in 2020.

That's 20 years earlier than the Social Security fund is expected to become insolvent, and - boomers: are you getting this? - only 14 years away.

The Employee Benefit Research Institute is reporting that today's typical Medicare-covered retired couple needs $295,000 in the bank just to cover health care throughout retirement. And that's assuming that they have Medicare to depend on.

The bottom line? That retirement savings plan you're contributing to every month is not just for green fees and gifts for your grandchildren; it's for doctors' visits and medicine. It makes sense to save and invest more than the minimum, and think about earmarking some of your money for health care.

One of the best ways is using a high-deductible health care savings account now as your medical insurance.

If your employer offers one, that's great. If not, consider buying one on your own instead of using your company's insurance plan. It might be a good idea if your employer-provided plan is not that good or if you see job changes in your future.

If you have one of these high-deductible insurance plans, without a second policy, you can use it to accumulate health-earmarked savings for retirement.

These plans let you salt away as much as $5,450 for couples ($2,700 for singles), plus an extra $700 a year for anyone over 55. The money you contribute is tax deductible; when you withdraw it to pay for health care, it is not taxable. That makes it better than tax-deferred retirement accounts.

You can shop for HSAs at a few different Web sites, including http://www.hsainsider.com, http://www.hsafinder.com and http://www.ehealthinsurance.com.

Put the money in, but don't use it for your annual health care expenses. Let it grow until you retire, when you really need extra cash for health care.

Consider an HSA that comes with an investment account, so you can put the money in something likely to grow faster than a bank account. Look for one that allows easy and inexpensive investing in mutual funds.

What if you're not eligible for an HSA? Just invest in after-tax dollars so you'll have more cash ready when the cartilage in your knees and the federal health care budget both start wearing away at the same time.

You can simply buy a low-fee index mutual fund or a low-fee exchange traded mutual fund for your HSA. Both of these investments track movements of a stock index for a fraction of what you'd pay for active management. With that HSA cap, you won't have enough money for the first few years to build a diversified portfolio any other way.

There's also a certain logic to indexing your health care savings to health care costs. It's not exactly a proxy for health care inflation, but it might come close. As health care companies become more and more profitable, your health care investments in them will go up and up.

You can do that by investing in a health index fund or a mutual fund that focuses on health care companies. Some to consider are Fidelity Select Pharmaceuticals (FPHAX, up almost 18 percent in a year, according to Morningstar); Vanguard Health Care, (VGHCX, up almost 15 percent), or T. Rowe Price Health Sciences (PRHSX, up 10.43 percent).

Exchange traded funds that focus on health care stocks include Vanguard Health Care Vipers (VHT), Health Care Select Sect SPDR (XLV), and the iShares S&P Global Healthcare Sector (IXJ).

And remember to take good care of yourself. Yeah, yeah, you've heard it before. But those bad health habits you're sneaking by with now are really going to cost you in 2020.

(Linda Stern is a freelance writer. Any opinions in the column are solely those of Ms. Stern. You can e-mail her at lindastern(at)aol.com.)

Investment Social Security