Red-haired women were significantly more likely than were women with nonred hair to have elevated levels of C-reactive protein that may increase risk for cardiovascular conditions, according to data from nearly 9,000 women participating in the Nurses’ Health Study.
“Positive associations between red hair and cardiovascular disease and cancer in women, but not men, have been reported,” wrote Rebecca I. Hartman, MD, of Brigham and Women’s Hospital, Harvard Medical School, Boston, and colleagues.
In a study published in the Journal of Investigative Dermatology, they reviewed data from the Nurses’ Health Study, a 1976 cohort study of 121,700 women registered nurses in the United States. They analyzed blood specimens from 8,994 women that were collected between 1989 and 1990. Participants’ natural hair color was determined by asking them their natural hair color at age 21 years, with choices of red, blonde, light brown, dark brown, or black. Overall, dark brown/black hair was the most common color (45%) and 390 of the women (4.3%) had red hair.
The average CRP levels were significantly higher for women with red hair (3.7 mg/L), compared with those with blonde (3.3 mg/L), light brown (3.0 mg/mL), or dark brown/black (3.2 mg/L).
Using the CRP levels for red-haired women as a reference, women with blond, light brown, and dark brown/black hair averaged significantly lower CRP levels than those of red-haired women in an age-adjusted model (–15.2%, –18/1%, and –14.2%, respectively) and in a multivariate analysis (–12.7%, –14.1%, and –10.9%, respectively).
Non-red-haired women had significantly lower odds of high CRP levels compared with red-haired women, with odds ratios of 0.62, 0.60, and 0.67 for women with blonde, light brown, and dark brown/black hair, respectively, in multivariate analysis, the researchers found.
The study was limited by several factors including the use of self-reports for hair color and the relative homogeneity of the Nurses’ Health Study, which has a population of mostly white, female health professionals, the researchers noted.
However, the findings of significantly increased CRP levels “could potentially explain a prior report of increased risks of cardiovascular disease and cancer in red-haired women,” they said. “Although, we observed similar associations in the NHS between red hair and cardiovascular disease and cancer, they were not statistically significant,” they added.
Additional studies are needed to validate and examine the clinical significance of the results, they concluded.
“Elevated CRP levels, a marker of inflammation, have been associated with increased risk for several diseases, including colon cancer and heart disease,” lead author Dr. Hartman said in an interview. “Another study suggested red-haired women have elevated risks of cardiovascular disease and cancer. We wanted to see if different levels of inflammation in red-haired women could possibly explain these findings.”
She said she was not surprised by the findings, “as they were in line with our hypothesis.” In addition, “animal studies suggest that the gene most responsible for red hair, MC1R, may be linked to inflammation,” she said.
While red-haired women were found to have higher CRP levels in the study, “the underlying mechanism and clinical significance remain unknown,” and more research is needed, Dr. Hartman emphasized. “First, our findings need to be validated in women and also examined in men. If our findings are validated, future studies should examine the mechanism of CRP elevation in red-haired women, and whether these women have elevated risks of colon cancer and heart disease,” she said.
“If red-haired women do have increased levels of inflammation, and as a result have elevated risks of colon cancer and heart disease, then future interventions can focus on enhanced screening and possibly chemoprevention in this population,” she added.
The study was supported by the National Institutes of Health. Lead author Dr. Hartman was supported by an American Skin Association Research Grant.
SOURCE: Hartman RI et al. J Invest Dermatol. 2020 Oct 12. doi: 10.1016/j.jid.2020.09.015.