A new study has revealed that the number of middle-aged white Americans dying is increasing during the recent years.

According to the researchers, this group has the highest mortality rate in the country compared to other age and ethnicity-based groups, New York Times reported.

The study was conducted by a group of researchers from Princeton University based on the data obtained by the Centers for Disease Control and Prevention. Based on the data collected from 1999 to 2013, the death rate for middle-aged white Americans increased by more than one percent each year.

On the other hand, the mortality rate for Hispanics and blacks belonging in the same age group annually dropped by two percent during the same period, CNN has learned.

The researchers were surprised with their findings since they expected to see an overall drop in mortality rates.

"We have come to expect mortality rates in the middle age to continue to decline, which they did throughout most of the 20th century," Ann Case, an economics professor at Princeton University and co-author of the study said in a statement

"It was really a surprise to see a sustained period when mortality rates actually increased (among middle-aged white Americans)," she added.

Upon conducting further investigations regarding the alarming trend, the researchers were able to identify the major factors responsible for the increasing mortality rate.

According to the researchers, the leading causes of deaths for middle-aged white Americans are drugs, suicide, alcohol and liver disease. The researchers explained that these factors affect members of this group especially those with a lower level of education.

The researchers also noted that the fall in household incomes also contributed to the disposition of members of this group. Due to hardships such as these, many of them turn to alcohol or drugs as a way of coping with their problems. As for those who can't seem to handle their personal troubles, many of them turn to suicide.

In fact, according to researchers, suicide accounts for 81 percent of overall deaths among middle aged white Americans who do not have a bachelor's degree or higher, the Guardian reported.

The researchers also noted that if this trend continues, those who survive through middle age will suffer more because of their health as they get older.

"This is not automatic," the researchers wrote in the study. "If the epidemic is brought under control, its survivors may have a healthy old age."

"However, addictions are hard to treat and pain is hard to control, so those currently in mid-life may be a 'lost generation' whose future is less bright than those who preceded them," they added.

The findings of the researchers were detailed in a report published on November 2 in the journal Proceedings of the National Academy of Sciences of the United States of America.