(Reuters Health) - - Health insurance saves lives thats the conclusion of a report released on Monday, just in time to weigh into the debate among Senate Republicans considering a bill that could strip millions of Americans of coverage.

Overwhelming scientific evidence shows that lack of insurance is sometimes deadly, co-author Dr. David Himmelstein, a professor at the City University of New Yorks Hunter College School of Public Health, said in an email.

Based on findings from a variety of large studies, Americans without health insurance faced 40 percent higher odds of dying during the study periods than the privately insured, the report published in the Annals of Internal Medicine found.

Being uninsured is deadly, co-author Dr. Steffie Woolhandler, a Hunter College health policy professor, said in a phone interview. That was the conclusion from a 2002 Institute of Medicine report. The evidence thats accumulated over the last 15 years actually strengthens the Institute of Medicines conclusions.

Since the institute, an independent panel of experts, issued its 2002 report, new studies have examined the impact of health insurance on mortality. Woolhandler and Himmelstein reviewed the more recent research and found that having private insurance, when compared to being uninsured, reduced the odds that Americans would die during the studies by as much as 29 percent, Woolhandler said in a phone interview.

But Bernard Black, another researcher whos looked at the issue, questioned the methodology used in most other studies and attacked the new reports conclusions as completely invalid. Almost all the studies compared uninsured to privately insured Americans and excluded people with public insurance.

Its not a proper research design, Black, a professor at Northwestern Universitys Pritzker School of Law in Chicago, said in a phone interview. The core mistake lets take the sick people out of the equation.

Woolhandler called Bakers view clearly an outlier. Most of the researchers removed publicly insured Americans from their analyses because people frequently go on public insurance when they become disabled, and therefore, including the publicly insured would muddy the results and fail to clarify whether having insurance kept people alive, she said.

Consequently, researchers generally have compared uninsured people to privately insured people while trying to control for variables that might impact mortality, such as poverty and health status, she said.

It would be unethical to study the question by randomly insuring some Americans and not others. But a lottery for insurance in Oregon did create something akin to the gold standard of a randomized controlled trial.

In 2008, the state held a lottery and allowed poor, healthy, uninsured adults to sign up for Medicaid. For every 10,000 people who enrolled in the health insurance program, 13 lives were saved, the study found.

The results were not statistically significant, although Woolhandler said she believes that was because the study had too few subjects. But, she said, If you save 13 lives for every 10,000 people you insure, for me, as a doctor, thats really meaningful.

On Monday, the American Medical Association registered its opposition to the proposed Republican Senate healthcare bill. If enacted, the physicians group said the legislation would make it harder for low- and middle-income Americans to afford healthcare and would violate the precept of first, do no harm. (bit.ly/2tN3udt )

While most researchers believe loss of coverage would result in more deaths, the question of mortality benefits from insurance remains unresolved for Black. Its not like Im saying there is no effect, he said. Im saying we dont know, and lets go look.

The question of mortality is not the only question facing members of Congress as they consider reforming healthcare, said Dr. Matthew Davis, a professor at Northwestern Universitys Feinberg School of Medicine.

Even before this study, members of Congress and the American public who elected them already have a strong personal sense of the value of health insurance, he said in an email.

I have had uninsured patients who were grateful they survived a health problem even though they did not have coverage, but I have never had a patient who told me that the reason they survived is that they were uninsured, he said.

The Senates healthcare proposal aims to undo former President Barack Obama s signature healthcare law, which has provided coverage to 20 million Americans since 2010. The bill would repeal the 3.8 percent net investment income tax on high earners and would phase out Obamacares expansion of the Medicaid program for the poor.

SOURCE: bit.ly/2fazTFW Annals of Internal Medicine, online June 26, 2017.