"We know that people are living longer and the general population is getting older, but that doesn't fully explain the increase we saw in the death rate in people with Parkinson's," study author Wei Bao, MD, PhD, who conducted the research at the University of Iowa in Iowa City. "Understanding why more people are dying from this disease is critical if we are going to reverse the trend."

The study looked at a national death registry that included 479,059 people who died of Parkinson's between 1999 and 2019.

After adjusting for age, researchers found that the number of people who died from the disease increased from 5.4 per 100,000 people in 1999 to 8.8 per 100,000 people in 2019. The average annual increase was 2.4%.

Researchers found mortality increased significantly across all age groups, both sexes, various racial and ethnic groups and different urban-rural classifications. However, death rates were twice as high in men as in women. Bao says one possible explanation for this sex difference is that estrogen, which leads to higher dopamine levels in parts of the brain that control motor responses, may protect women from developing Parkinson's.

White people were more likely to die from Parkinson's than other racial and ethnic groups. In 2019, the death rate for white people was 9.7 per 100,000 people, followed by Hispanic people, at 6.5 per 100,000 people, and non-Hispanic Black people, at 4.7 per 100,000 people. Bao said previous studies have shown that compared to white people, Black and Hispanic people are less likely to see an outpatient neurologist, due to socioeconomic barriers, suggesting that white people may have a higher chance of receiving a Parkinson's diagnosis.

"It's important to continue to evaluate long-term trends in Parkinson's death rates," Bao said. "This can inform future research that may help pinpoint why more people are dying of the disease. Also, updating vital statistics about Parkinson's death rates may be used for priority setting and financing of health care and policy."

A limitation of the study is that only one underlying cause of death was recorded on each death certificate, so only people who were recorded as having died of Parkinson's were included in the study. This may not accurately reflect the prevalence of the disease as a cause of death.