Volume 5, Number 1: Spring Equinox, 2003

Fluid Retention During the Menstrual Cycle - BC Diabetes Foundation

Colin White

Summer Research Intern, Division of Endocrinology, University of British Columbia


I recently received a scholarship from The BC Endocrine Research Foundation (BCERF( to work as a student intern. I just graduated from Memorial University of Newfoundland and this was an excellent opportunity for me to get some research experience before I started medical school in September. I spent six weeks working with the Centre for Menstrual Cycle and Ovulation Research (CeMCOR) analyzing changes in fluid retention across the menstrual cycle. Fluid retention is a sub clinical sign that varies in intensity depending on what phase of the menstrual cycle an individual woman is in. This is largely reported anecdotally among women. Despite this common and well-known physiological interaction, published scientific literature is sparse on the topic. The issue of fluid retention associated with the menstrual cycle is a topic that may give a better understanding of women’s health. CeMCOR took the initiative to investigate this systematically. A review of the previous literature showed that virtually no published articles dealt with fluid retention as a natural process. Most research dealt with fluid retention as part of a disease such as studies of “premenstrual syndrome” or as a side effect of oral contraceptives. These articles do not investigate the fact that fluid retention occurs in healthy women and that there was a need for documentation of this sign in a normal population. Commonly women’s body weight fluctuates by as much as 2.5 kg during a menstrual cycle. Some of the fluctuation is hypothesized to be due to fluid retention. It is believed that the ovarian hormone, estrogen, promotes fluid retention through interactions with the renin-aldosterone-angiotension pathway. This pathway leads to fluid accumulation throughout the body. Another ovarian hormone, progesterone, is hypothesized to inhibit fluid retention.

The data for this analysis were collected by 61 healthy women over one year. The women recorded their basal body temperature (BBT) every day for one year. They also completed a daily menstrual cycle diary that included a score for their feeling of fluid retention (on a scale of 0 to 4). The women also belonged to one of three exercise groups. They were normally active women (non-exercising), women who were participating in regular exercise (constant runners), and women who were increasing exercise intensity in training for a marathon. Using a statistical algorithm (quantitative basal temperature analysis), the date of temperature rise was calculated from the BBT. From this, ovulation and length of cycle phases were determined. The documentation of ovulation in the cycles was a unique feature of this analysis because it is quite common to see published articles that fail to report ovulation occurrence. This actually is a major mistake in that it has been shown that ovulation does not occur every menstrual cycle and it seems likely that the physiological changes in ovulatory cycles may not occur. All days of the menstrual cycles were broken down into one of two categories. The perimenses period was 10 days long and centered on the first day of flow; the remaining days of the cycle were classified as midcycle.

What Were the Key Questions?

We had three questions: (1) Does fluid retention differ between midcycle and perimenstrual days? (2) Are there differences between ovulatory and non-ovulatory cycles? (3) Is there a difference in this pattern by exercise group?

This research adds to the understanding and expanding knowledge base that CeMCOR is working towards. The issue of fluid retention and normal cyclic patterns has possible implications on women with high blood pressure, those participating in fitness or exercise programs or those trying to understand more about their physiological patterns. A scientific manuscript is in preparation summarizing this study. The Centre aims to educate both the public and the scientific community about women’s health and natural body rhythms.

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