Cannabis smoking and serum C-reactive protein: a quantile regressions approach based on NHANES 2005-2010

Abstract

Background: Pre-clinical studies link cannabinoid-1 receptor activation to inflammation and atherosclerotic effects; anti-inflammation and immunosuppression seem to be mediated by cannabinoid-2 receptor activation. In this epidemiological study, we aim to present estimates on suspected cannabis-attributable immunomodulation as manifest in serum C-reactive protein (CRP) levels as non-specific inflammatory markers with interpretable clinical values. With strength of data from recent large nationally representative community sample surveys, the research approach illustrates value of a quantile regressions approach in lieu of the commonly used but relatively arbitrary cutpoints for CRP values.

Methods: The study population encompasses 20-59 year old participants from the National Health and Nutrition Examination Surveys, 2005-2010 (n=1115 recently active cannabis smokers and 8041 non-smokers, identified via confidential Audio Computer Assisted Self-Interviews). Age, sex, race, education, income-poverty ratio, alcohol consumption, and tobacco smoking also were measured, together with body mass index (BMI), which actually might be on a mediational path. Quantile regressions, with bootstrapping for variance estimation, made it possible to hold these covariates constant while estimating cannabis-CRP associations.

Results: Evidence suggesting possible cannabis-attributable immunomodulation emerges at CRP levels below the median (p<0.05). Whereas BMI might help explain a cannabis link with serum CRP, but BMI-stratified analyses disclosed no appreciable variation of the cannabis-CRP relationship across BMI subgroups.

Conclusions: Extending pre-clinical research on cannabis-attributable immunomodulation, this study's CRP evidence points toward possible anti-inflammatory effects of cannabis smoking. More definitive evidence can be derived by combining pre-clinical research, studies of patients, and epidemiological research approaches.

Keywords: CRP; Cannabis smoking; Immunomodulation; Inflammation; NHANES.

Figure 1

Estimated Effect of Recently Active Cannabis Smoking on Serum CRP (mg/L) Levels Across the Quantile Range of Serum CRP Levels, With Those who Never Smoked Cannabis as a Reference Subgroup. Data for the US Based on the National Health and Nutrition Examination Survey 2005–2010.

1. By definition, the x-axis median is at 0.5 -- i.e., 50% of the population above and below that point

2. Estimates adjusted for age (years), sex (male/female), ethnic self-identification (ESI: coded for non-Hispanic White/non-Hispanic Black/Hispanics/all others), educational attainment (coded for less than high school/high school/above high school), income-poverty ratio (coded for less than 1 versus 1 or more), tobacco cigarette smoking (coded for never/past/current), and past-year alcohol consumption (coded for yes/no)