In this trial the effects of 30 mg betacarotene and 25000 units vitamin A retinyl palmitate were weighed against placebo using 18314 men and women 22 of the study population had earlier been exposed to asbestos 39 had been smokers and 60 were currently smokers

Add punctuation
In this trial the effects of 30 mg beta-carotene and 25,000 units vitamin A (retinyl palmitate) were weighed against placebo using 18,314 men and women. 22% of the study population had earlier been exposed to asbestos, 39 % had been smokers, and 60 % were currently smokers.