How old are you? Well, if you’re black, you can add three years to that number.

That’s the conclusion of a disturbing new study, which suggests “racial differences in the pace of aging” appear to be a key reason why black Americans tend to die at younger ages than whites.

“Our results showed that, on average, blacks tend to be more than three years older biologically than whites,” report Morgan Levine and Eileen Crimmins of the University of Southern California’s Davis School of Gerontology. “This is consistent with findings from previous studies reporting that blacks tend to have levels of biological risk factors that are indicative of someone significantly older chronologically.”

The study, published in the journal Social Science and Medicine, uses data from the third National Health and Nutrition Examination Study. It specifically looks at 7,644 Americans—89 percent white, 11 percent black—who underwent physical exams and completed lifestyle surveys between 1988 and 1994. (Hispanics and Asians were excluded from the study.)

As study participants grew older, the gap between blacks' and whites' biological and chronological ages widened until they "were nearing old age, after which it began to converge."

The researchers calculated each participant’s “biological age” by looking at 10 biomarkers that have been linked to aging, including C-reactive protein, serum creatinine, glycosylated hemoglobin, systolic blood pressure, and total cholesterol. They also noted their body-mass index, level of education, and whether they were present or former smokers.

“On average, the biological age for blacks was 53.16 years,” compared to 49.84 years for whites, the researchers report. After controlling for socioeconomic status and health behaviors (they note that obesity rates are higher for blacks than whites, and excess weight can “contribute to progressive breakdowns in biological tissues and systems”), this gap shrank somewhat, but was still pronounced: 52.72 years for blacks, compared to 49.89 years for whites.

Previous researchers have pointed to the corrosive influence of racism as a possible explanation for the poorer health of blacks in America. A small study released in January found blacks who had experienced racism and come to accept (even unconsciously) the concept of racial inferiority had shorter leukocyte telomeres—a different biomarker of aging.

Levine and Crimmins did not attempt to measure negative health effects of racism, but their results are consistent with the theory. They point out that blacks “experience more discrimination, have less economic security, and often live in worse neighborhoods” than whites, all of which can lead to “higher levels of both physical and psychological stress, with the potential to cause a myriad of biological changes with respect for aging.”

“Everyday stressors associated with being black may negatively impact physiological functioning and, under chronic exposure, accumulate over the lifespan and contribute to growing disparities in biological risk,” they write. “Furthermore, if such environmental, behavioral, and mental factors contribute to an acceleration of the aging process, we would expect that persons who are aging the fastest should have the highest risk of mortality, and thus (have a) lower life expectancy.”

That’s exactly what the data shows. As study participants grew older, the gap between blacks' and whites' biological and chronological ages widened until they "were nearing old age, after which it began to converge,” the researchers write. “This suggests the most disadvantaged blacks may be accumulating poorer and poorer health as they age,” ultimately dying at earlier ages than otherwise similarly situated whites.

But whatever the causes, “being black is associated with significantly higher biological age,” the researchers conclude, “and that this is a pathway to early death.”