Caffeine intake, tolerance, and withdrawal in women: A population-based twin study

Objective: Caffeine is by far the most commonly consumed psychoactive subst ance. The use and abuse of most other licit and illicit psychoactive drugs have been shown to be substantially heritable. However, the impact of genet ic factors on caffeine consumption, heavy use, intoxication, tolerance, and withdrawal is largely unknown. Method: Caffeine consumption, in the form o f brewed coffee, instant coffee, tea, and caffeinated soft drinks, as well as caffeine intoxication, tolerance, and withdrawal, were assessed by perso nal interviews of 1,934 individual twins from female-female pairs ascertain ed from the population-based Virginia Twin Registry. The sample included bo th members of 486 monozygotic and 335 dizygotic pairs. Twin resemblance was assessed by probandwise concordance, odds ratios, and tetrachoric correlat ions. Biometrical model fitting was also performed. Results: The resemblanc e in twin pairs for total caffeine consumption, heavy caffeine use, caffein e intoxication, caffeine tolerance, and caffeine withdrawal was substantial ly greater in monozygotic than in dizygotic twin pairs, Model fitting sugge sted that twin resemblance for these measures could be ascribed solely to g enetic factors, with estimated broad heritabilities of between 35% and 77%. Conclusions: Caffeine is an addictive psychoactive substance, Similar to p revious findings with other licit and illicit psychoactive drugs, individua l differences in caffeine use, intoxication, tolerance, and withdrawal are substantially influenced by genetic factors.