An analysis of data from two large prospective cohorts indicate that a healthier lifestyle is associated with a lower risk of developing rheumatoid arthritis (RA). Jill Hahn, ScD, MS, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health, Boston, and colleagues conclude from this finding that a substantial proportion of RA may be preventable by a healthy lifestyle. They published their findings online Jan. 18 in Arthritis Care & Research.1
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The team used a healthy lifestyle index with five modifiable, healthy lifestyle practices:
- Not smoking cigarettes;
- Maintaining normal weight (i.e., not being overweight or obese);
- Getting regular physical activity;
- Drinking alcohol only in moderation; and
- Following a healthy diet, low in saturated fats and carbohydrates.
Whereas past studies have demonstrated that not following each of these healthy lifestyle behaviors was individually associated with an increased risk of developing RA, the current study examined the factors in a continuing scale known as the Healthy Lifestyle Index Score (HLIS).2 Previous research has shown that adherence to such lifestyle guidelines contributes to health and protects against cancer and cardiovascular diseases.3–5
Hahn et al. analyzed cohorts that had detailed lifestyle data and lengthy follow-up. The 107,092 women in the Nurses’ Health Study (NHS, 1986–2016) and Nurses’ Health Study 2 (1991–2017) had a mean age of 43.7 years and a mean follow-up of 24 years per participant. The investigators identified 1,219 women with RA (776 seropositive and 443 seronegative). The condition had developed over 4,467,751 person-years. They found that women with the healthiest HLIS (i.e., 5) tended to be younger (mean = 41.1 years old) and live in U.S. census tracts with higher median household incomes (i.e., $51,887 median annual household income). Healthier women who were postmenopausal also tended to use hormones more than women with the least healthy HLIS score (i.e., 0). The least healthy women had a mean age of 46.7 years and a median annual household income of $41,959.
The team found that a higher (i.e., healthier) HLIS was associated with a lower overall, seropositive and seronegative RA risk (hazard ratio [HR] 0.86, 95% confidence interval [CI] 0.82–0.90; HR 0.85, 95% CI 0.80–0.91; HR 0.87, 95% 0.80–0.94, respectively). This association remained true even after adjusting for potential confounders, such as age, median family income parity, breastfeeding and hormone use.
The investigators then performed sensitivity analyses by lagging the physical activity exposure variable by four years behind the RA outcome assessment window. They did this to test the possibility that preclinical RA was causing less physical activity or an increase in body mass index (BMI). The findings did not change, and the researchers concluded from this finding that their analysis was not identifying reverse causation.