Obesity as a risk factor for slowing of sensory conduction of the median nerve in industry. A cross-sectional and longitudinal study involving 429 workers.

As part of a longitudinal study of the etiology of carpal tunnel syndrome in industry, we evaluated weight and body mass index (BMI) as risk factors for slowing of sensory conduction of the median nerve. Using nerve conduction studies, we evaluated 858 hands of 429 industrial workers in 1984 and reevaluated 630 hands of 316 of these same workers in 1989. Weight and BMI were strongly and positively correlated with the maximum latency difference (MLD). In 1984 and 1989 the risk for abnormal nerve conduction averaged 3.5-fold and 4.1-fold greater, respectively, in the obese workers than in the slender workers. In stepwise regression analysis for 1989 MLD based on 1984 factors, the BMI was the number one factor selected, followed by age, wrist depth/width ratio, hand dominance, and exercise level. None of three 1984 job-related factors (occupational hand use, duration of employment, or industry) was an independent predictor of 1989 MLD. This study suggests that individual characteristics, not job-related factors, are the primary determinants of slowing of sensory conduction of the median nerve and carpal tunnel syndrome.