Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some global health-care companies to your portfolio, the iShares S&P Global Health Care ETF (NYSEMKT:IXJ) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.48%. It yields about 2.1%, as well.

This ETF has a bit of a mixed performance  record, beating the world market over the past three and five years, but slightly lagging it over the past decade. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

With a low turnover rate of 6%, this fund isn't frantically and frequently rejiggering its holdings, as many funds do.

Why global health care?
With our planet's population growing and aging and living longer, and many economies developing, it's safe to say that there's likely to be plenty of demand for medical devices over the years ahead.

More than a handful of health-care companies  had strong performances over the past year. Gilead Sciences (NASDAQ:GILD), for example, surged 94%, and recently hit a 52-week high. Known for its HIV treatments, it has been expanding its scope, most notably into hepatitis treatments. A hep-C treatment recently yielded strong results in clinical testing, boosting the stock, and results so far for HIV treatments are also encouraging.

Eli Lilly (NYSE:LLY) gained 41% over the past year. The company received FDA approval  a few months ago for its radioactive agent Amyvid, used to help detect Alzheimer's, and treatments for lung cancer and diabetes 2 have also been approved. Like most big pharma companies, it faces patent expiration challenges -- but it's also big enough to buy some smaller companies, along with their promising pipelines. Some don't see the company as exciting right now, but its future may be bright. Patient investors can collect a 4.1% dividend as well.

Merck (NYSE:MRK) advanced 40%, partly on approval of a new insomnia drug, as well as excitement over drugs in clinical trials that tackle lung cancer, ovarian cancer, and osteoporosis, plus a new vaccine for human papillomavirus. The stock also yields 3.8%. On the downside, Merck is losing patent protection for its asthma blockbuster, Singulair.

Celgene (NASDAQ:CELG) gained 30%. Its stock took a hit back in June, when it withdrew its approval application in Europe for its multiple myeloma drug, Revlimid. But it gained on good results for its pancreatic drug, Abraxane. Some see Celgene as an attractive acquisition target because of its pipeline, while others are just happy to see it growing briskly, with third-quarter revenue up 14%, for example.

The big picture
Demand for global health care isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.