By Samantha Blady
A study published in Genome Biology in August 2016 supplies the first analysis of the epigenetic clock across different racial groups. By analyzing blood, saliva, and brain samples, epigenetic aging rates were compared among seven different racial groups and in men and women. As discovered in the study, rates of epigenetic aging are significantly associated with race and gender.
This study was based on paradoxical tendencies among gender and race. Women tend to have lower mortality rates yet show higher rates of developing disease when compared to men. After adjusting for socioeconomic disadvantage, racial groups show different mortality rates. In the United States, Hispanics have a higher cardio-metabolic risk than Caucasians, yet they also have a higher life expectancy.
The Epigenetic Clock
The epigenetic clock is based on 353 epigenetic markers and measures the epigenetic age of a certain cell, tissue, or organ. The unprecedented accuracy of the epigenetic clock in measuring chronological age has shown to predict mortality. In a past study, offspring of people who lived over 105 had epigenetically younger blood than others of the same age. The epigenetic clock has been used in research on obesity, HIV, Down’s syndrome, Parkinson’s disease, Alzheimer’s, lung cancer, and lifetime stress. In this study, researchers use the epigenetic clock to analyze relationships between epigenetic age, life expectancy, and cardio-metabolic risk among gender and race.
Blood, saliva, and brain samples were taken from Caucasians, Hispanics, East Asians, Tsimane Amerindians, and people of African ancestry. Epigenetic age was measured using the Ilumina Infinitum 450K. A “universal measure” of epigenetic age acceleration was defined as the difference between epigenetic age values of samples and values predicted from a model for Caucasians. This measure can be defined in most cells and tissues other than sperm.
IEAA vs. EEAA
IEAA (Intrinsic Epigenetic Age Acceleration) is a measure of epigenetic aging that measures intrinsic changes and does not include extracellular changes in blood cell counts. EEAA (Extrinsic Epigenetic Age Acceleration) measures epigenetic aging effects including extracellular changes in blood cell counts and immune-related aging, and is thus a better measure.
Results
After analyzing samples, researchers found that
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Hispanics and Tsimane Amerindians have a lower IEAA but higher EEAA than Caucasians.
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African Americans have a lower EEAA than both Caucasians and Hispanics.
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Education level is negatively associated with higher EEAA
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EEAA is strongly associated with the rain forest habitat in African populations, but IEAA is not.
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IEAA and EEAA from blood tissue do not predict coronary heart disease but are weakly associated with risk factors.
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Epigenetic aging rates in women are slower than those in men.
The Paradoxes
The Hispanic paradox is echoed in this study as Hispanics have a lower IEAA than Caucasians despite their higher cardio-metabolic risk. As is currently being studied, this contradiction may be due to differences in the Hispanic immune system.
The black-white mortality crossover is echoed in this study as well. Mortality rates are higher in blacks than in whites in younger age but are lower in black men and women aged 85 and older. This observation is paralleled by the finding of a lower EEAA in older African-Americans when compared to Caucasians in this study.
The Tsimane inflammation paradox states that high levels of inflammation in Tsimane are not associated with cardiovascular aging. This finding is consistent with the lower rate of IEAA in Tsimane found in this study. However, a low life expectancy is still reported. A higher EEAA is consistent with the observation that elevated inflammation ultimately depletes T cells and deteriorates the immune system, leading to the low life expectancy of Tsimane.
The sex morbidity-mortality paradox holds that despite higher rates of comorbidity in women, mortality rates are lower in women than in men. Consistent with this paradox, epigenetic aging rates are faster in men than in women. Epigenetic markers of blood, saliva, and brain tissue show higher vulnerability in males of all racial groups.
Overall, this study provides data that shows how epigenetic aging rates differ among racial groups as well as between men and women. This study is the first to directly compare and contrast epigenetic rates of aging among races and ethnicities.
And, although, much of the science of epigenetics still remains to be revealed, this study does provide interesting insight into epidemiological paradoxes.