President Obama's health care law aims to expand insurance coverage to 25 million Americans by 2016. But expanding health insurance isn't necessarily the same thing as increasing access.

As the major provisions of the health care law go into effect in 2014, several elements threaten to limit Americans’ access to care.

Obama's health care program boosts the number of Americans with insurance by offering subsidies to individuals to purchase policies on government-run exchanges and by expanding the number of people who are eligible for Medicaid.

But Medicaid pays doctors significantly less than private insurance or even Medicare, making doctors less likely to accept beneficiaries as patients.

A study by the National Center for Health Statistics, published in 2012 by Health Affairs, found that 31 percent of doctors were not accepting Medicaid patients in 2011, though the numbers varied by state.

In California, for instance, 43 percent of doctors weren't accepting new Medicaid patients, and in New Jersey, the number was a staggering 60 percent.

Though the health care law temporarily increased Medicaid payment rates for primary care doctors, the increase expires at the end of this year.

As for individuals who obtain health insurance on one of the new exchanges, they’re likely to find themselves in a plan with a narrower network.

To offset the costs of the new requirements imposed on insurance policies to make them more comprehensive, insurers cut payment rates to doctors and hospitals. Nationwide, this has translated into fewer choices for Americans.

Last year, a McKinsey & Co. analysis of 955 Obamacare plan offerings in 13 states found that almost half had narrow networks.

Just a few plans offer access to the nation's top medical institutions, such as Memorial Sloan-Kettering Cancer Center in New York and Cedars-Sinai in Los Angeles.

Defenders of the law could argue that for uninsured Americans gaining coverage for the first time, even restricted access of Medicaid and the exchange plans are a vast improvement. But the same can’t be said for all Americans.

To start, millions of Americans who saw their existing plans canceled as a result of changes stemming from the health care law will be forced to seek coverage that offers fewer choices.

Additionally, one of the ways in which the health care law plans to offset the $1.8 trillion cost of expanding coverage is to extract savings from Medicare.

But in a May 2013 report, Paul Spitalnic, the acting chief actuary of the Centers for Medicare and Medicaid Services, warned that as a result of the cuts, “Medicare prices would be considerably below the current relative level of Medicaid prices, which have already led to access problems for Medicaid enrollees, and far below the levels paid by private health insurance.

“Well before that point, Congress would have to intervene to prevent the withdrawal of providers from the Medicare market and the severe problems with beneficiary access to care that would result.”

The law also includes $156 billion in payment cuts to privately administered Medicare Advantage plans. In December, Kaiser Health News reported that UnitedHealthcare — the nation’s largest Medicare Advantage insurer — was dropping thousands of doctors from its network.

However, the extent to which the law causes access problems can only be truly known over time. One of the broader challenges for the law is that it plans on adding tens of millions of people to the insurance rolls at a time of attrition in the medical profession, with no credible plan to increase the system’s capacity. In fact, when it comes to the number of physicians in America, trends are moving in the wrong direction.

In March 2013, a Deloitte survey found “six in 10 physicians say that it is likely that many physicians will retire earlier than planned in the next one to three years.” A 2012 survey by Jackson Healthcare projected “significant” attrition among American physicians in the coming years, with more than a third of doctors planning to leave medicine within a decade.

So much for Obama’s June 2009 vow to Americans that, “If you like your doctor, you will be able to keep your doctor, period.”