Real estate investment trusts, or REITs, have their fair share of fans and critics.

On one hand, income investors favor these investments as important sources of high dividend yields. On the other hand, those bearish on REITs probably see a difficult future on the horizon in the form of higher interest rates.

Nowhere is this constant tug-of-war more evident than in the share price performance of many REITs over the past couple of years. There has been a high level of volatility in stock prices of REITs, which only adds another layer of confusion as to when, and if, to buy.

Here are two great reasons to consider buying these health-care focused REITs, HCP (PEAK -0.17%) and Health Care REIT (WELL 0.56%).

The unstoppable force of shifting demographics
Baby boomers, or those born roughly between 1946-1964, are the single largest generation in the United States. Baby boomers alone constitute about one-third of the U.S. adult population. There are millions of people entering retirement every year, and as the general population ages, this will place an enormous need on health care.

Aside from pharmaceutical companies themselves, HCP and Health Care REITs are great picks because they operate a slew of health-care related properties. HCP and Health Care REIT are both involved in acquiring and leasing health-care related properties, such as senior housing, medical facilities, and hospitals.

It goes without saying that the aging population in the United States will serve them well. Tens of millions of people are in or nearing retirement, and will require lots of health care services.

In addition, HCP and Health Care REIT hold diversified portfolios. Health Care REIT is diversified geographically across the United States, Canada, and the UK. Meanwhile, HCP has balanced assets. Its assets under management are spread across five categories. It derives 36% of its portfolio from senior housing, and another 28% from skilled nursing facilities, 17% from life science buildings, and 16% from medical office buildings.

What this means is that both HCP and Health Care REIT hold high-quality asset bases that provide solid cash flow and steady growth. The core financial metric for REITs is funds from operations, rather than traditional earnings per share. This is a non-GAAP equivalent that provides a clearer picture of REIT's underlying performance.

On this basis, it's clear that HCP and Health Care REIT are well-run businesses.

HCP grew funds from operations by 1% last quarter, due in part because the comparison period benefited from a one-time gain from sales of marketable securities. Excluding this, FFO grew a more satisfactory 4%. For its part, Health Care REIT posted 10% growth in funds from operations last quarter and produced a company record.

These growth rates allow for both companies to raise their dividends year in and year out.

High dividends and long track records of shareholder rewards
In today's environment of low interest rates and high stock prices, yield is hard to find.

The yield of the overall market, as measured by the S&P 500 Index, is only about 2%. Fixed-income investments won't do you much better. The yield of the 10-year U.S. Treasury Bond is just HCP happens to be the only REIT included in the S&P 500 Dividend Aristocrats index, and recently raised its dividend for the 29th year in a row.

Likewise, Health Care REIT recently paid its 171st consecutive quarterly dividend, and earlier this year raised its payout by 4%.

Both HCP and Health Care REIT offer very strong yields in this low-yield climate. HCP yields 5.2%, and Health Care REIT pays approximately 5%. These two companies can provide valuable income for those seeking dependable payouts, and both increase their dividends above the rate of inflation every year. That means your purchasing power will be protected even if inflation hits, instead of eroding as it would with fixed-income securities.

The Foolish bottom line
In today's environment of record-high stock prices and historically low interest rates, income investors are in a bind. While yield might seem hard to find, one sector income investors should be considering is REITs.

In particular, HCP and Health Care REIT are two specific ones that you should consider because they're about to reap huge rewards from the long-term demographics of the United States. Millions of Americans are entering retirement with each passing year. The aging population will require lots of health care, and that's great news for HCP and Health Care REIT.