Long-term care insurance really is long term: buying a policy commits you to pay premiums over decades. If you stop those payments, thousands of dollars you have already spent might as well have gone down the drain.

A new study suggests that is exactly what a sizeable number of policyholders are doing -- allowing their policies to lapse.

More than one-third of long-term care insurance (LTCI) policyholders who buy policies at age 65 or older let their coverage lapse sometime in their lifetime, according to a study by the Center for Retirement Research at Boston College (CRR).

The study concludes that individuals most likely to let a policy lapse are those who need the coverage most -- those with cognitive impairment, and might soon need care, or those with low income and wealth, who would be in financial jeopardy in a medical crisis.

Long-term care insurance covers expenses for nursing home or home care if you become incapacitated -- most of which is not covered by Medicare and can be extremely expensive out of pocket. The annual cost of a private nursing home room this year is $91,250, according to an annual survey by Genworth, the largest underwriter of these policies.

The CRR findings come at a time with the long-term care insurance industry is struggling. In 2014, new sales of individual policies fell 22 percent from 2013, to $316 million, according to LIMRA, an insurance industry research and consulting group. That sales pace is less than half what it was a decade earlier (2004). Fewer than 8 percent of Americans over age 50 own private LTCI, according to LIMRA.

Defenders of the industry have been pushing back against the CRR report. Industry data suggests that no more than 1 percent or 2 percent of policies are allowed to lapse in any given year. But CRR widened out the lense to the long view.