The effect of abstinence from smoking on urinary excretion of hydroxyproline

The effect of abstinence from smoking on the urinary hydroxyproline to creatinine ratio (HOP ratio) was assessed in 49 smokers who participated in an anti-smoking course. Urine samples were collected at the beginning of the course and weekly during the subsequent 14 weeks in 1985. The subjects were divided into five groups depending on the number of cigarettes smoked daily before abstinence: 1-10, 11-20, 21-30, 31-40 and greater than 40 cigarettes. The urinary HOP ratio immediately after abstinence from smoking was proportional to the mean daily number of cigarettes smoked in the past. All groups showed decreasing HOP ratios with a longer period of abstinence. Half of the total decrease observed in the HOP ratios after 14 weeks was reached within 5 or 6 weeks. When using the Brinkman index to adjust for the number of smoking years, half of the maximum decrease in all groups was reached within 4 weeks. In an exponential decay model fitted to the data, the half-life time taken to reach the non-smokers' level was 9-10 weeks for all groups. The HOP level of smokers who smoked less than 41 cigarettes before cessation approached the HOP level of the control group after 61-74 weeks. The results suggested that the urinary HOP ratio was useful as a biochemical marker for short-term breakdown of lung collagen and lung elastin.