By Yeganeh Torbati

WASHINGTON (Reuters) - The suicide rate among American veterans has increased by nearly a third since 2001, a bigger rise than in the wider population of the United States, a U.S. Department of Veterans Affairs study released on Wednesday said.

The report estimated that an average of 20 veterans a day died from suicide in 2014, or about 7,300 in the year, compared to a previous estimate of 22 a day. But researchers have cautioned against relying too heavily on that figure to indicate trends in suicides because it does not take into account that the overall number of veterans is declining because of deaths from old age.

For the first time, a study of veteran suicides drew from 55 million veterans' records from 1979 to 2014 and from every U.S. state, the report said. Previous studies were more limited in scope and drew from three million records from 20 states or from records of those using veterans health services.

The study found that between 2001 and 2014, veteran suicides increased by 32 percent, while civilian suicides increased by 23 percent in the same time period. After controlling for factors like age and gender, this meant veterans faced a 21 percent greater risk for suicide than those who had not served in the armed forces.

The report did not provide numbers associated with the percentages it recorded and a department representative could not immediately be reached to provide more information.

While the suicide rate was highest among younger veterans, aged 18 to 29, most veteran suicides - 65 percent - in 2014 were among those 50 or older..

The study found sharp differences between the suicide rates of those veterans who used VA services compared to those who did not, though it did not draw conclusions about why. Of an estimated 21.6 million veterans in the United States, about 8.5 million receive VA health services, the report said.

Suicide rates for male veterans who used VA services increased by 11 percent since 2001, compared to a 35 percent increase among those who did not. That contrast was even sharper for female veterans. The rate of suicide among female veterans since 2001 increased 4.6 percent for those who used VA services, and increased 98 percent for those female veterans who did not.

As a whole, the risk of suicide among female veterans was 2.4 times higher than among civilian women in 2014, the study found. By contrast, male veterans faced an 18 percent higher risk for suicide than their civilian counterparts in 2014.

(Reporting by Yeganeh Torbati; editing by Grant McCool)