Did you know that your bones aren’t static, but are actually very dynamic? Bones are constantly going through a remodelling process, and this process is under the influence of a complex group of hormones including parathyroid hormone, calcitriol, and calcintonin, as well as estrogen and progesterone. This article will look in depth at how bone changes throughout a woman’s life, what role specifically estrogen and progesterone (and their fluctuations) play in bone health, and what you can do to ensure bone health at all ages of life.
The Remodelling Process:
The remodelling of bone consists of bone resorption (breakdown) and formation (building). When these two processes are equal, bone mineral density (BMD) remains stable (in homeostasis). When formation > resorption, BMD increases, and when resorption > formation, BMD is lost.
Without getting too into the complex physiology of the bone remodelling process, I want to mention a couple of cells that are important (this will be relevant in regards to hormonal influence). Osteoblasts are the cells that make the organic matrix of bone and then mineralize bone (add to BMD), while osteoclasts are the cells that resorb bone. Both of these cells are under the influence of hormones, cytokines, and local factors.
Life cycle of bone:
Before we look at age-specific recommendations for bone health, it’s important to understand how bone changes throughout a person’s life. In childhood, and especially in adolescence, we see a rapid increase in size and mineral density of bone (called bone modeling, this growth happens until mature height is reached). At this time, formation is greater than resorption, and typically peak bone mass occurs in the late teens and early twenties (age 16-19 for hip and femoral BMD and 30-33 for lumbar spine).
During the reproductive years (from about mid-twenties to early fifties), bone mineral density is generally in homeostasis (you do lose a bit during this time, about 0.3-0.5% per year). Peak bone mass is maintained until perimenopause, when the rate of decline in bone mineral density accelerates. This is when resorption becomes greater than formation. Bone loss does continue, but the rate slows after about the age of 70.
Osteoporosis, which literally translates to “porous bone,” occurs when there is so much bone loss that bones develop holes (or become porous). While there are many factors that play into this (hormonal changes, low calcium or Vitamin D levels, and sedentary lifestyles to name a few), in general this can happen for two reasons: peak bone mineral density is lower earlier in life (there is less bone to lose) or bone resorption occurs at a rapid rate (bone is lost more quickly). This means that what occurs earlier in a woman’s life will affect bone health later in life – more on that below.
Relationship of Bone to Estrogen and Progesterone:
How do estrogen and progesterone affect bone mineral density? Estrogen has been studied extensively and shown to be important for maintenance of bone mineral density. In general, estrogen slows bone loss by modulating the activity of osteoclasts (the cells responsible for bone resorption) and a deficiency of estrogen can lead to accelerated bone loss (1) (this in part explains the increased bone loss in menopause). Progesterone, on the other hand, directly stimulates osteoblasts (the cells that build bone) (2).
Importantly, these hormones fluctuate monthly throughout a woman’s cycle (for a refresher on these changes, see my previous post) – estrogen is highest in the first half of the cycle, peaking around Day 14, while progesterone rises in the second half of the cycle. When estrogen drops after the Day 14 peak, this can cause increased osteoclast activity and ultimately result in slight bone resorption. For this reason, progesterone and its bone-building effects are essential in the second half of the cycle to balance that estrogen drop and subsequent bone resorption. Recall that ovulation is necessary for the creation of progesterone, meaning that anovulatory cycles or a lack of period can negatively impact the estrogen/progesterone balance, as well as bone mineral density. These effects were shown in a study that examined the relationship between ovulatory disturbance and spinal bone loss: their findings showed that in women with regular, ovulatory cycles their spinal bone density remained the same, while in women with at least one anovulatory cycle per year (where ovulation did not occur), spinal bone loss was about 4% per year and in those with multiple short luteal phases (second half of the cycle), bone loss was 2% per year.
What this means for various life stages:
Just as bone changes throughout a person’s life, recommendations for specific life stages will also vary. Let’s take a look:
Adolescence
This is the time when bone modeling is greatest and when we are building up peak bone density. This will set the stage for bone health later in life: greater BMD at peak bone mass means a lesser likelihood of fractures in our elder years. During this time, it is important to follow general and lifelong guidelines for bone health including plenty of weight-bearing exercise, maintaining a healthy BMI, ensuring adequate intake of in calcium, magnesium, Vitamin D, and Vitamin K, and keeping alcohol and cigarette smoking to a minimum. Equally important is to recognize hormonal fluctuations during adolescence and support the body’s endogenous production of these hormones in balance. Often, oral contraceptive pills (OCPs) are prescribed during adolescence, not only as a contraceptive, but also for painful periods, PMS and acne – but they are not without their side effects. OCPs contain supraphysiological dosages of synthetic hormones (greater than what the body produces), which can suppress the body’s own hormonal production and this can negatively affect peak bone mass and lifelong bone health. In fact, a recent 2-year study looked into the effect of OCPs on BMD and concluded that adolescents that used OCPs demonstrated less peak bone mineral density in comparison to those who were not on OCPs (4). This OCP-associated reduction in peak bone mass is a very important consideration for lifelong bone health!
Reproductive Years:
This is the plateau phase – a balance of bone formation and resorption. The general guidelines outlined above remain – keep exercising and maintaining a healthy and nutritious diet. The other piece to consider is how the menstrual cycles, and balance of estrogen and progesterone, affect bone health. In order to maintain bone homeostasis, both estrogen and progesterone are needed. Recall that anovulation (irregular periods, no periods, and occasionally periods that look normal but may be anovulatory) as well as shortened cycles can lead to progesterone deficiency. The first step is to know if you’re ovulating – for more on how to track this, check out my previous article. If you’re concerned that you may not be ovulating, connect with a health care practitioner you feel comfortable working with to discuss your concerns and treatment options.
Perimenopause & Menopause:
During perimenopause, both estrogen and progesterone levels begin to decline, with progesterone declining more rapidly (resulting in a high estrogen state). In menopause, we see either a gradual or sharp decline in estrogen, leading to a low estrogen state. Both of these can lead to imbalances of estrogen and progesterone. During these years, hormone replacement therapy (HRT) can be considered for the prevention of osteoporosis. Several studies have investigated the benefit and risk of HRT – both estrogen and progesterone – for the prevention of osteoporosis (5, 6). The North American Menopause Society released a position statement in 2017 that listed several key points about HRT and prevention of osteoporosis, including:
Hormone therapy prevents bone loss in healthy postmenopausal women, with dose-related effects.
Hormone therapy effectively prevents post-menopause osteoporosis and fractures. (7)
Please note that HRT is not for everyone, as certain contraindications do exist. Please consult your healthcare practitioner to discuss the benefits and risks of HRT.
Of course, the general recommendations remain here, too: keeping a healthy diet with adequate calcium, magnesium, Vitamin D, and Vitamin K, maintaining a healthy BMI, moderate weight-bearing exercise, and minimal alcohol and smoking.
My hope is that this information is valuable for you in making informed decisions around your health. If you are concerned about your hormonal or bone health, or if you suspect that your hormones may be out of balance, connect with a health care practitioner to discuss this. It is essential to have a proper workup done and to be well-informed of the benefits and risks of any treatment. If you’d like to discuss your bone health, hormones and treatment options, consider booking an appointment at Juniper Family Health.
Wishing you health and well-being!
References:
1. Väänänen, H. and Härkönen, P. (1996). Estrogen and bone metabolism. Maturitas, 23: 65-69.
2. Prior, J. (1990). Progesterone as a bone-trophic hormone. Endocrin Rev, 11(2): 386-398
3. Prior, J. et al. (1990). Spinal bone loss and ovulatory disturbances. New England Journal of Medicine, 1;323(18):1221-7.
4. Brajic, T. et al. (2018). Combined hormonal contraceptives use and bone mineral density changes in adolescent and young women in a prospective population-based Canada-wide observational study. Journal of Musculoskeletal and Neuronal Interactions, 18(2): 227-236.
5. Gambacciani, M and Levancini, M. (2014). Hormone replacement therapy and the prevention of postmenopausal osteoporosis. Przeglad Menoauzalny, 13(4): 213-220.
6. Prior, J. (2018). Progesterone for the prevention and treatment of osteoporosis in women. Climacteric, 21(4): 1-9.
7. The North American Menopause Society. (2017). The 2017 hormone therapy position statement of The North American Menopause Society. Menopause: The Journal of the North American Menopause Society, 24(7): 1-26