This article was written by one of our contributors; PhD student and founder of The Period of the Period – Kelly McNulty.
A background to bone health
We often perceive bone to be a static tissue whereby relatively little change occurs in its structure across our lifespan. However, contrary to popular belief our bones are living, active tissues that are constantly being broken down and remodelled. In females, 90 to 95% of skeletal bone mass occurs by age 18 , but this doesn’t peak until about the age of 30. After that, bone loss occurs faster than bone formation and this process happens faster (and at a younger age) in females, making us more susceptible to osteoporosis and fractures.
The influence of hormones on bone health
Bone turnover (aka the balance between bone resorption and bone formation) is modulated partly by our hormones. Of primary importance for female bone health is the hormone oestrogen as this plays a vital role in the development and maintenance of bone mineral density (BMD). For instance, many studies have highlighted that oestrogen deficiency, for example after the menopause (i.e., women lose between 2 to 3% of bone mass per year after menopause) and those with hypothalamic amenorrhoea (i.e., amenorrhoeic women will lose approximately 2 to 3% of bone mass per year if the condition remains untreated), can result in poor bone health. Additionally, testosterone is also important for bone health in women (and men) and has a direct effect on bone formation and maintenance, as well as indirectly strengthening bones and bone density by stimulating muscle growth.
Hormonal contraception & bone health
Hormonal contraception (e.g., oral contraceptive pills, injections, implants, the patch, the vaginal ring, and intrauterine systems) are used by many females for the purpose of preventing an unplanned pregnancy as well as other reasons such as alleviating the symptoms of the menstrual cycle. Hormonal contraceptives work by altering the naturally occurring menstrual cycle by changing our internal hormonal milieu. For example, they provide exogenous (synthetic) oestrogens and progestins, which act on the hypothalamic-pituitary-ovarian axis (or HPO axis for short) by negative feedback meaning that concentrations of endogenous (natural) oestrogen and progesterone are downregulated. Because of this altered hormonal profile it’s possible that hormonal contraception might therefore influence bone health. As such, the effects of hormonal contraceptives on bone health in exercising females has been a topic of increased interest, particularly over the last few years. So, what does the research say?
Combined hormonal contraception:
This refers to any hormonal contraception that contains both synthetic oestrogens and progestins (i.e. the combined oral contraceptive pill, the vaginal ring, and the patch). The majority of evidence from premenopausal adult women suggested no differences in BMD between combined oral contraceptive users and non-users[6-7], although there are some studies which have found both positive and negative effects of combined oral contraceptive use on BMD. The mixed findings might be explained by different study designs, methods, and population as well as different formulations and time of combined oral contraceptive use. Indeed, there appears to be a difference in findings between low-dose combined oral contraceptives and those with 20 to 30 μg ethinyl oestradiol, with low-dose combined oral contraceptives more likely to have a negative impact on BMD. Additionally, studies of teen girls and young adult women, generally indicate that combined oral contraceptive use can compromise BMD when compared to non-users. Although again it’s important to note that any effect seems to be mainly determined by the dose of synthetic oestrogen. Finally, other combined hormonal contraceptive forms, such as the vaginal ring and the patch have not been well researched for their effect on bone health and further research is needed before conclusions can be made.
Progestin-only hormonal contraception:
This refers to any hormonal contraception that contains only one synthetic hormone – progestins (i.e., the progestin-only pill, the implant, the injection, and intrauterine systems). Of these methods, the research highlights that none of these forms of hormonal contraception appear to affect bone health (although data for these methods is limited), except for the progestin-only injection. Specifically, some studies highlight that women – both adult women and teen girls – using the progestin-only injection lose BMD (on average 5 to 7% in the hip and spine with this loss occurring more rapidly in the early years of use and reduces after 2 years) whilst they are using this type of hormonal contraception. Therefore, it’s thought that the progestin-only injection induces a state of hypoestrogenism that leads to increased bone resorption and a decrease in BMD. As such, there are two groups of women who are typically not advised to use this method of hormonal contraception; teenagers (as their bones are still growing) and women who enter menopause whilst using this type of contraception (due to concerns about bone health and fracture risk). Additionally, those with risk factors for osteoporosis might also be advised against this method, but this is a conversation and decision to be made by you and your doctor/GP. On the flip side the good news is that these decreases in BMD have been shown to be largely or completely reversible once discontinued.
*A note on the use of hormonal contraception in the treatment of amenorrhea, oligomenorrhea, and low bone density: It’s recommended from the research that the first line of treatment for those suffering from components of the female athlete triad should be to improve BMD and resume normal menses through nutritional and behavioural changes over the use of hormonal contraceptives.
Make an impact
We can reduce the risk of poor bone health and therefore the likes of osteoporosis by adopting lifestyle choices that increase peak bone mass in our teen years and reduce bone loss in adult years. For instance, factors that improve bone health include nutrition (i.e., consuming the right combination of protein, calcium, vitamin D, magnesium, vitamin K and phosphorus. For more information see article ‘Diet & Bone Health’) and regular weight-bearing and muscle-strengthening exercise. Specifically, high-impact and weight-bearing exercise such as walking, running and bodyweight exercises are advocated to be one of the best tools to increase bone mass and prevent its loss.
*Advice from the Royal Osteoporosis Society is that regular physical activity is a safe and effective way to help strengthen your bones and reduce your risk of fracture in the future if you have already been diagnosed with osteoporosis, or have risk factors. If you have a fracture, or at a high risk of one, you might need to avoid certain high-impact activities. It’s always good to speak to your doctor/GP to determine what types of activity are best suited for you.
Females of all ages and abilities should be aware of the importance of bone health not only for performance and training purposes, but more importantly for their health and maintenance of an active lifestyle across their lifespan. The evidence relating to hormonal contraceptive use and bone health is inconclusive, as results from the available studies to date are conflicting and further high-quality research is needed. Overall, it’s likely the effect of hormonal contraception on BMD depends on the type of hormonal contraception used and the individual. As such, if you are feeling unsure about your bone health, the best advice for now is to talk to your doctor/GP.
The content provided here is for informational purposes only and is not intended to substitute medical advice provided by your usual medical provider.
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