Chronic inflammation as a determinant of future aging phenotypes

Abstract

Background: The importance of chronic inflammation as a determinant of aging phenotypes may have been underestimated in previous studies that used a single measurement of inflammatory markers. We assessed inflammatory markers twice over a 5-year exposure period to examine the association between chronic inflammation and future aging phenotypes in a large population of men and women.

Methods: We obtained data for 3044 middle-aged adults (28.2% women) who were participating in the Whitehall II study and had no history of stroke, myocardial infarction or cancer at our study's baseline (1997-1999). Interleukin-6 was measured at baseline and 5 years earlier. Cause-specific mortality, chronic disease and functioning were ascertained from hospital data, register linkage and clinical examinations. We used these data to create 4 aging phenotypes at the 10-year follow-up (2007-2009): successful aging (free of major chronic disease and with optimal physical, mental and cognitive functioning), incident fatal or nonfatal cardiovascular disease, death from noncardiovascular causes and normal aging (all other participants).

Results: Of the 3044 participants, 721 (23.7%) met the criteria for successful aging at the 10-year follow-up, 321 (10.6%) had cardiovascular disease events, 147 (4.8%) died from noncardiovascular causes, and the remaining 1855 (60.9%) were included in the normal aging phenotype. After adjustment for potential confounders, having a high interleukin-6 level (> 2.0 ng/L) twice over the 5-year exposure period nearly halved the odds of successful aging at the 10-year follow-up (odds ratio [OR] 0.53, 95% confidence interval [CI] 0.38-0.74) and increased the risk of future cardiovascular events (OR 1.64, 95% CI 1.15-2.33) and noncardiovascular death (OR 2.43, 95% CI 1.58-3.80).

Interpretation: Chronic inflammation, as ascertained by repeat measurements, was associated with a range of unhealthy aging phenotypes and a decreased likelihood of successful aging. Our results suggest that assessing long-term chronic inflammation by repeat measurement of interleukin-6 has the potential to guide clinical practice.

Figure 1:

Selection of participants for the current analyses from the Whitehall II study cohort. *Age cutoff chosen to allow follow-up beyond age 60 for surviving participants.

Figure 2:

Multivariable logistic regression of associations between interleukin-6 (IL-6) levels at baseline (A) and over a 5-year exposure period (B) and subsequent aging phenotypes at 10-year follow-up. Aging phenotypes were: successful aging (v. normal aging, cardiovascular disease [CVD] event and non-CVD death phenotypes combined), total n = 3044; CVD event (v. successful and normal aging phenotypes combined), total n = 2897 (excludes 147 participants who died of non-CVD causes); and non-CVD death (v. successful and normal aging phenotypes combined), total n = 2723 (excludes 321 participants who had fatal or nonfatal CVD event). For model A, IL-6 levels were separated into 3 categories: low (≤ 1.0 ng/L), intermediate (1.1–2.0 ng/L) and high (> 2.0 ng/L). For model B, IL-6 was measured twice (5 yr before baseline and at baseline); 0 = neither measurement was high, 1 = either measurement was high, 2 = both measurements were high. Odds ratios (ORs) were adjusted for sex, age, socioeconomic status, smoking status, physical activity, acute inflammation and use of anti-inflammatory drugs; values greater than 1.0 indicate an increased likelihood of the outcome. CI = confidence interval, ref = reference group.