Temperature regulation in women: Effects of the menstrual cycle

Abstract

Core body temperature changes across the ovulatory menstrual cycle, such that it is 0.3°C to 0.7°C higher in the post-ovulatory luteal phase when progesterone is high compared with the pre-ovulatory follicular phase. This temperature difference, which is most evident during sleep or immediately upon waking before any activity, is used by women as a retrospective indicator of an ovulatory cycle. Here, we review both historical and current literature aimed at characterizing changes in core body temperature across the menstrual cycle, considering the assessment of the circadian rhythm of core body temperature and thermoregulatory responses to challenges, including heat and cold exposure, exercise, and fever. We discuss potential mechanisms for the thermogenic effect of progesterone and the temperature-lowering effect of estrogen, and discuss effects on body temperature of exogenous formulations of these hormones as contained in oral contraceptives. We review new wearable temperature sensors aimed at tracking daily temperature changes of women across multiple menstrual cycles and highlight the need for future research on the validity and reliability of these devices. Despite the change in core body temperature across the menstrual cycle being so well identified, there remain gaps in our current understanding, particularly about the underlying mechanisms and microcircuitry involved in the temperature changes.

Keywords: Circadian rhythm; estradiol; exercise; follicular; luteal; ovulation; progesterone; thermometer; thermoregulation; wearable temperature sensor.

Figure 1.

Reproductive hormone and basal body temperature changes across an ovulatory menstrual cycle. Top panel shows the profile for serum luteinizing hormone (LH) that peaks just before ovulation (dotted line). Middle panel shows fluctuations in serum levels of the ovarian hormones, estradiol, and progesterone across the menstrual cycle. Bottom panel indicates the biphasic curve in morning basal body temperature (oral) across the menstrual cycle. Data from 10 women with ovulatory menstrual cycles [58].

Figure 2.

Data represent rectal temperatures recorded every minute for 4 h before bedtime (time 0) and 20 h after from fifteen young women (age: 22 ± 4 years) in the mid-follicular and mid-luteal phases of their menstrual cycles. Women had serum progesterone levels in the luteal phase reflective of ovulatory menstrual cycles. Subjects followed their usual daytime schedules and spent the night in a sleep laboratory. Modified from [65].

Figure 3.

Basal body temperatures (5-min rectal temperature taken in the early morning) averaged over 5 days before any hormones were administered (pre-progesterone), during daily progesterone injections (5 mg or 10 mg, intramuscular), for 3 days when estradiol dipropionate (1.0 mg) was injected together with progesterone, and for 5 days after ending hormone administration, in 6 men. *p < 0.01 compared with the pre-progesterone condition; # p = 0.04, compared with progesterone condition. Data from [98].

Figure 4.

The threshold core body temperature for effector responses in the follicular and luteal phase of the menstrual cycle. Top panel shows the threshold for sweating, middle panel shows the threshold for cutaneous vasodilation, and the lower panel shows the thresholds for shivering (a) and increasing metabolic rate (b). Interventions are (1) during exercise in the early morning [126], (2) during exercise in the late afternoon [126], (3) during passive heat exposure [125], (4) during exercise in the heat [123], (5) during exercise [123], (6) during exercise [30], (7) during passive heat (upper and middle panels) or cold (lower panel) exposure [29], (8) during exercise [138], and (9) during exercise [139]. Core body temperatures are esophageal, rectal, or calculated mean body temperature.