Those with the habit of going to sleep early show a higher ratio of lymphocytes while those with the habit of staying up late show a higher ratio of granulocytes.

In this study, we examined the effect of the difference in time of going to sleep on the numerical values of leukocyte subsets and various hormones. Subjects consisted of 26 healthy adults (15 men, 11 women) with a mean age of 37.6 years. Among the 26 individuals, 12 persons (Group E) were of the habit of going to sleep before midnight consistently, while 14 persons (Group L) were of the habit of staying up late, consistently going to sleep after 2 am. For Group E, it was found that the ratio of lymphocytes was remarkably high in comparison with Group L (Group E 41.6 +/- 2.54%, Group L 31.7 +/- 2.03%, P < 0.01). On the other hand, for Group L it was found that the ratio of granulocytes was remarkably high in comparison with Group E (Group E 53.0 +/- 2.51%, Group L 62.3 +/- 2.22%, P < 0.01). However, no difference was observed in lymphocyte and granulocyte ratios due to the duration of the sleep. As the excessive quantity of granulocytes was not corrected through longer sleep, these findings suggest that the time when first going to sleep is more important than the total hours of sleep achieved.