The average person believes testosterone to be essential for muscle growth. But it’s a mistake to overlook how important estrogen is for muscle gain. Despite popular belief, estrogen is essential for muscle growth. Estrogen levels that are too high or too low could cause a deficiency in muscle quality. The steady level of estrogen supplied by contraceptives could also affect the ability to grow muscle tissue. The amount of estrogen affects the development of muscles in women and those who take oral contraceptives may be at a disadvantage in building muscle compared to women who menstruate naturally.
By Mallory Warner
Estrogen is the dominant female hormone and has been shown to increase muscle mass and strength. This has been shown in studies of women in menopause. When women start menopause, their estrogen levels decrease dramatically by 75%. A 2010 study showed that women had a significant decrease in muscle strength when they began menopause and continued to decline thereafter. This decline could not be associated with muscle atrophy because the data were based on the maximum force that could be produced by the muscle’s cross-sectional area. A 2010 study conducted on 10,000 post-menopausal women found that the women taking estrogen-based hormone therapy had approximately 10% greater muscle mass than women who were not taking the hormone. This is evidence to suggest that estrogen levels have a positive effect on muscle quality.
Estrogen has also been shown to increase the amount of collagen stored in the body. Collagen helps with muscle growth because it boosts the production of creatine in muscles and aids in increasing the body’s fat-free mass and muscle strength. Collagen muscle-tendon synthesis is also positively affected by estrogen where it can help in the bioavailability of the insulin-like growth factor-1. Research on this correlation was conducted in 2009. They compared women on birth control pills to women menstruating naturally by analyzing the amount of estrogen affecting bone, tendons, and muscle connective tissues through collagen synthesis. Their results concluded that oral contraceptive use in women had a diminishing effect on the bioavailability of IGF-1 and an impeding consequence on collagen synthesis.
The amount of estrogen in female bodies can vary depending upon age and the decision to use oral contraceptives. In a normal menstrual cycle, the average estrogen levels start at around 19 pg/ml and increase up to 410 pg/ml during ovulation. However, post-menopausal women have less than 35 pg/ml of estrogen. Surprisingly, women who are taking the birth control pill have even lower estrogen levels at approximately 10-30 pg/ml! The use of low-dose estrogen in oral contraceptives was driven by a few studies in the 1980s that linked high levels of estrogen to increased risk for cardiovascular diseases. Although other more recent research has found no such correlation, there have not been sufficient studies on the subject to change the perception of the connection. In fact, estrogen levels are required to be low in the birth control pill to suppress ovulation to decrease the chance of becoming pregnant. However, low levels of estrogen are not without consequence. A 2019 study found that “estrogen deficiency induces apoptosis in skeletal muscle contributing to loss of mass and thus strength.” The study suggested that a lack of estrogen creates a disruption in mitochondrial pathways and mitochondrial DNA turnover. This disruption results in upregulated cell death causing apoptosis.
Inflammation and interference with satellite cell function also contribute to the decrease in muscle strength when estrogen is deficient. One 2019 study concluded that, after injury, muscles had a greater recovery rate from inflammation due to the abundance of neutrophils brought on by increased estrogen levels. Neutrophils help prepare the inflamed site for tissue repair by the macrophages. Because estrogen levels increase the rate and number of neutrophils acting on inflamed muscles, muscle mass and strength recovery can be accelerated. It appears that estrogen has a direct impact on the contractile proteins vital for muscle strength because of the effect it has on myosin chains. Muscle fibers were tested in a 2013 study on sets of post-menopausal twins. Sisters who were on estrogen hormonal therapy experienced greater force per crossbridge than sisters who were not on hormonal therapy. This suggests that estrogen may enhance muscle contraction due to the rate of force production on myosin chains.
Few studies have been conducted on muscle development comparing naturally menstruating women to women on oral contraceptives. However, one study from 2009 concluded that there is a connection between oral contraceptives and impaired muscle gain. The study compared women on oral contraceptives to women menstruating naturally over a 10-week resistance training program. The results found that women who menstruated naturally produced 60% more muscle mass after the 10 weeks than those who were taking oral contraceptives. They then further discovered that birth control pills are associated with low levels of dehydroepiandrosterone (DHEA), the adrenal gland hormone that is partially responsible for producing estrogen. The researchers also found that oral contraceptives produced high levels of cortisol which inhibits protein synthesis and causes the body to use muscle as a source of energy. This link between low levels of estrogen caused by the amount of DHEA and the abundance of cortisol in women who were taking birth control pills, may explain why muscle growth is hindered by oral contraceptives.
Ultimately, it has been shown that estrogen has a positive effect on muscle gain and strength in studies of post-menopausal women and twins. Low estrogen seems to have a very negative effect on muscle function. In oral contraceptives, this could be due to the low levels of DHEA and/or the low dose of estrogen contained in birth control pills. Estrogen deficiency can lead to multiple muscular issues including delayed contraction speed, slow recovery process, apoptosis, and a low rate of collagen synthesis. While minimal research has been completed on the consequences of oral contraceptives in relation to muscle growth, birth control pill’s low levels of estrogen, high cortisol levels and low DHEA levels may be the cause of impaired muscle growth. Hopefully, future studies can be completed to explain the reasons behind the inconsistency in muscle growth between naturally menstruating women and those on oral contraceptives.
Collins, B. C., Laakkonen, E. J., Lowe, D.A., (2019). Aging of the musculoskeletal system: How the loss of estrogen impacts muscle strength. Bone.123, 137-144. Retrieved November 18, 2021 from Science Direct database.
Hansen, M., Miller, B. F., Holm, L., Doessing, S., Peterson, S. G., Skovgaard, D., et al., (2009). Effect of administration of oral contraceptives in vivo on collagen synthesis in tendon and muscle connective tissue in young women. Journal of Applied Physiology, 106(4):1435-43. Retrieved November 30, 2021 from the National Library of Medicine.
Lee, C. W., Newman, M. A., Riechman, S. E., (2009). Oral contraceptive use impairs muscle gains in young women. Retrieved November 18, 2021 from the Federation of American Societies on Experimental Biology database: https://doi.org/10.1096/fasebj.23.1_ supplement.955.25
Lowe, D. A., Baltgalvis, K. A., Greising, S. M., (2010). Mechanisms behind estrogens’ beneficial effect on muscle strength in females. Exercise and Sport and Science Reviews, 38(2) 61-67. Retrieved November 16, 2021 from the US National Public Library of Medicine National Institutes of Health database.
Qaisar, R., et al. Hormone replacement therapy improves contractile function and myonuclear organization of single muscle fibres from postmenopausal monozygotic female twin pairs. Journal of Physiology, 591 (9) (2013), pp. 2333-2344
Thomas, Liji (2018). Estradiol Measurement. Retrieved November 16, 2021 from News Medical Life Sciences web site:https://www.news-medical.net/health/Estradiol-Measurement.aspx