Stocks? For retirement? Sounds a bit strange, doesn't it? We're always hearing about how stocks are supposedly too risky to depend upon for our golden years. But you need stocks -- not only leading up to retirement, but throughout your life.

A study recently released by the National Center for Health Statistics showed that the average life expectancy in the United States topped 78 this year for the first time ever. In fact, "U.S. life expectancy has been steadily rising, usually by about two to three months from year to year," according to the study.

What this means for you
This has huge implications for your retirement. You simply cannot afford to stash your retirement funds into conservative vehicles. With inflation eating away at those returns, you run the risk of outliving your nest egg.

Retirees should own stocks. If you jump out of the market, you'll leave behind one of the most effective wealth-building instruments ever … and you could end up facing a gruesome retirement scenario.

Park any short-term money (funds you expect to need in the coming five or so years) in more conservative places, such as CDs or money markets. Bonds, of course, also make up a key part of retirees' portfolios. But a good chunk should still be in stocks. (The Vanguard Target Retirement 2010 fund, for instance, invests in 54% stocks and 46% bonds.)

But which stocks? To get after that answer, let's look at some characteristics of stocks that could help support you in retirement.

1. Competitive advantages
This one may be obvious, but it's incredibly important: Invest in companies with sustainable competitive advantages. Your retirement dollars shouldn't go toward complex arbitrage situations or binary-outcome biotechs. Instead, they should support businesses with long-term advantages over their competitors.

These strengths can include strong brand names, economies of scale, network effects, high barriers against competition, and the cost to customers of switching to a competitor. Think of eBay (NASDAQ:EBAY), for example. Its rivals face an uphill battle in their attempts to usurp eBay's rule of the online auction market, because eBay already has a massive number of buyers and sellers. If you wanted to buy something over the Internet, eBay might number among your top options. If you wanted to sell, you'd probably find the most buyers there. Who would want to buy or sell at some Johnny-come-lately website?

In the retail world, Wal-Mart's (NYSE:WMT) size gives it a big advantage. It can be a tough negotiator with suppliers, demanding lower prices, since sellers can hardly go elsewhere to peddle their wares.

2. Dividend payers
Dividend payers make particularly good stocks to retire on. For starters, dividends are the only way you can get income from your stocks without selling them.

Dividends can also add some stability to your portfolio. The key here is to search for companies with a history of paying -- and hopefully increasing -- dividends to shareholders. Steady payouts suggest a level of fiscal responsibility and shareholder commitment that's important for a retirement portfolio.

Stocks with a history of increasing dividends also add a measure of protection against inflation -- something no retiree should ignore! Even though it's had a rough year, General Electric (NYSE:GE) is a dividend-hiker that currently pays a nice yield of 4.6%. Not coincidentally, GE's stock has been a long-term winner.

3. Defensive stocks
We're not talking about stocks that get all sulky and indignant at the tiniest perceived slight. Defensive stocks tend to weather the market's ups and downs more steadily than their peers. These companies' resilience makes them great stocks to own when the going gets tough.

Defensive sectors usually include utilities, consumer staples, health care, and, err, financials. (Maybe not so much for that last sector these days.) Defensive stocks tend to pay steady dividends, and they make reliable products that consumers buy even during economic tough times.

If the economy is in a recession, you'll still take your medicine, buy cans of soup, and use electricity. But you might not buy a car this year, or a new air conditioning system for your home. That makes Pfizer (NYSE:PFE) and Kraft Foods excellent examples of defensive companies; both happen to sport sizable dividend yields, too, at 7.3% and 3.7% respectively.

4. International picks
In an otherwise well-constructed portfolio, U.S.-based investors are generally underallocated to international stocks.

Most of us should include international holdings in our portfolios, not only because of their diversification benefits, but also because many offer enticing growth prospects.

China Mobile (NYSE:CHL), for example, has returned an annual average of more than 60% over the past three years, while Toyota Motors (NYSE:TM) has averaged nearly 11% (almost triple the S&P) over the past five.

If investing retirement funds in international companies makes you especially nervous, you can get quite a lot of international exposure via some American companies with extensive global operations. ExxonMobil (NYSE:XOM), for example, takes in some three-quarters of its revenue internationally.

The big picture
The perfect stock to retire on will have most, if not all, of the characteristics outlined above. Remember that many of the best companies to own during retirement aren't little, obscure ones -- as my colleague Seth Jayson has pointed out, you've most likely heard of "The 10 Best Stocks You Might Actually Buy."

You can get recommendations for solid and promising stocks and mutual funds in our Rule Your Retirement newsletter, along with critical and concise guidance on how to plan effectively for your golden years. It's the retirement resource I refer to most often, offering detailed discussions of topics such as asset allocation, estate planning, and safe withdrawal rates. I invite you to try it for free for a whole month. You'll gain access to all the past issues, including a host of "Success Stories" profiling people who retired early and are willing to share their strategies.

Longtime Fool contributor Selena Maranjian owns shares of General Electric, eBay, and Wal-Mart. Pfizer, and Kraft Foods are Motley Fool Income Investor recommendations. Wal-Mart and Pfizer are Motley Fool Inside Value picks. eBay is a Motley Fool Stock Advisor recommendation. The Motley Fool is Fools writing for Fools.