Nyctohemeral changes in plasma prolactin levels and their relationship to breast cancer risk

Abstract

The amount of prolactin has been determined in serial blood samples taken over 24 h from 20 pre- and 9 postmenopausal women volunteers. All women had a large increase in prolactin at night (24.00 h-03.00 h). A much smaller rise in prolactin occurred in the evening (18.00 h-20.00 h) which was just significantly different (p less than 0.05) from levels found in the afternoon. Prolactin concentrations at any given time in the 29 women were linearly correlated with corresponding levels in either of the adjacent time intervals. This correlation was highly significant (p less than 0.001) throughout 24 h, implying that a woman with a relatively high (or low) blood prolactin in the afternoon would have a similarly high (or low) concentration in the evening or at night. Premenopausal women had higher amounts of prolactin than postmenopausal volunteers throughout the day. Parity was found to be inversely related to prolactin levels in pre- and postmenopausal women; this effect was especially marked in the night peak of prolactin. In postmenopausal women an average of 33 years had elapsed since the birth of the last child, which implies that childbirth has a life-long effect on reducing prolactin levels. Thus the protective effect of early child-bearing and multiparity against developing breast cancer could be at least partly explained by these effects on serum prolactin levels.

Sex hormones in women in rural China and in Britain

“…The current results support this conclusion, but some caution should be maintained because bioassays may provide a better measure of HPr than do current radioimmunoassay methods (Rose et al, 1987b). HPr declines with increasing parity (Yu et al, 1981;Wang et al, 1984), but the effect is small beyond three births (Wang et al, 1987), so the difference in parity between the Chinese and British women in the current study would not have been expected to have a large effect on HPr.…”

“…SHBG falls during the night (Moore & Bulbrook, 1988) but does not vary significantly between morning and early evening (Key et al, 1990). HPr is high during the night and falls after waking (Gray et al, 1981), but rises a little during the afternoon and early evening (Wang et al, 1984), so that the direction of any bias between countries in our results for HPr is not clear. In a study in Finland (which is much further north than China), Kauppila et al (1987) found that mean E2 and T concentrations in premenopausal women were 13% and 12% lower respectively during the darkest months (November to January) than during the lightest months (May to June), so it is possible that the Chinese samples in the current study are a slight underestimate of year-round E2 and T. Kauppila et al (1987) found that seasonal changes in mean SHBG and HPr concentrations were negligible.…”

Clinical Stage of Breast Cancer by Parity, Age at Birth, and Time Since Birth: A Progressive Effect of Pregnancy Hormones?

“…Inconsistent findings in relation to female breast cancer risk (36-39) may be due to difficulties with sampling, owing to daily and monthly variations in prolactin levels (35,36,40). Serum prolactin levels are also considerably lower than breast fluid prolactin levels (41).…”

Progress in understanding breast cancer: Epidemiological and biological interactions

“…For this reason, it is interesting to note that serum prolactin levels are suppressed in young women in proportion to the number of children to which they have given birth [165]. There is also increasing evidence that estrogen receptor levels are inversely proportional to epidermal growth factor receptor levels [153].…”