Bone Health, Birth Control and the Female Athlete

The health of the skeletal system is crucial for all athletes no matter their age or experience level. However, an intense preoccupation with leanness and a low body fat percentage is extremely prevalent among the female athletic population, putting their health at risk – including bone health. Often both internal and external pressures result in a female taking her body to the extremes to meet such demands, resulting in menstrual irregularities, namely amenorrhea (You can read more about this here). Although the absence of menses (the menstrual cycle) may seem somewhat convenient for the female athlete, the consequences for the skeletal system are significant and concerning. Not only does this situation compromise an individual’s ability to achieve peak bone mass, it also may increase the risk of bone related injuries and potentially lead to osteoporosis in the long-term. Unfortunately, the process of bone loss is a silent one and often the athlete will be unaware of the problem until an injury occurs or medical testing reveals bone related conditions. At this time, the severity of the issue has likely reached a critical point with potentially irreversible consequences.

Bone health has a significant impact on an individual’s ability to lead an active lifestyle. Bone mineral density (BMD) reaches its peak in early adulthood, with 90% of peak bone mass gained by the age of 18 years, and begins to decline after menopause in women (1). The time when a female is reaching her peak bone mass is also the time she is most susceptible to eating disorders (such as anorexia and bulimia), poor nutrition, hypoestrogenism, and insufficient calcium intake (1). 

Although there is a strong genetic component to peak bone mass, an array of other modifiable factors such as exercise, diet, smoking, alcohol, medications and calcium intake also have a role to play (1). It is well established that physical activity is key to maintaining bone mass from childhood, through adolescence and into adulthood. Notably, maintaining bone mass has the potential to reduce fracture risk by 50% to 80% (1). However, another important consideration among female athletes is the impact of hormones and use of birth control on BMD.

Impact of hormones on bone health

A number of hormones can influence bone health, namely estrogen, testosterone and estradiol. Estrogen has a key role in skeletal homeostasis, with well recognized benefits on BMD. Estrogen is an inhibitor of bone turnover and helps to maintain the balance between bone resorption and formation. Both testosterone and estrogen are known to have positive effects on bone health by protecting against bone loss and slowing the rate of bone remodeling and their absence has been associated with an increased risk of osteoporosis. 

Estradiol is the primary form of estrogen found in the blood plasma (2). Many studies have consistently found very low or absent levels of estradiol when examining the hormonal profiles of amenorrhoeic athletes (2). This is extremely concerning given the role estradiol plays in the prevention of bone resorption and decrease in bone remodeling. Such findings also highlight the impact menstrual irregularities or the absence of menses can have for the female athlete. Looking at the various studies that have measured BMD in the spine, all report a significant decrease in vertebral BMD in the presence of menstrual irregularities. Amenorrhoeic athletes have been shown to have BMD values 9-31% lower than eumenorrheic women, which is far from ideal in the athletic world (2). A particularly interesting finding from one study showed significantly lower lumbar and total spine BMD in amenorrheic athletes compared to eumenorrheic athletes despite no difference in total body BMD. This finding not only further highlights the negative impact hormonal irregularities may have on bone health, it also supports the theory that athletic activity or exercise may be somewhat protective of the cortical bone, but trabecular bone, which comprises up to 42% of the lumbar vertebrae may not be so well protected (2). Cortical bone (or compact bone), which accounts for approximately 80% of the skeleton, is much denser compared to trabecular (or spongy) bone, which displays a greater degree of porosity (5-10% vs 50-90%). Cortical bone is found primarily in the shaft of long bones and encloses the trabecular bone at the end of joints and the vertebrae. Estrogen is protective of bone loss in both cortical and trabecular bone, therefore athletes experiencing menstrual irregularities where there is a deficiency of estrogen may be at higher risk of bone loss and bone-related issues. 

Birth control considerations

Birth control is commonly used among female athletes for various reasons. Aside from the most obvious reason for use being the prevention of unwanted pregnancy, birth control is often initiated to regulate a female’s menstrual cycle length, the consistency of the cycle or to manipulate the timing of the cycle, particularly around competition time. In some individuals, birth control may be used to manage heavy or painful periods or to control premenstrual symptoms. Birth control may also be utilised as a form of medical treatment to prevent or reduce bone loss in athletes with menstrual disturbances, such as oligomenorrhea and amenorrhea, both common among female athletes.

Types of birth control

There are many different types of birth control available. All types are based around synthetic versions of estrogen and progesterone and can be divided into two distinct groups:

• Combination – containing both synthetic estrogen and progesterone
• Progestin only – containing only synthetic progesterone

While these synthetic hormones act similarly to those naturally produced in the body, they are not identical. Synthetic estrogen is known to be significantly more potent than naturally produced estrogen, particularly in relation to its impact on a woman’s physiology. Progestins, as with naturally produced progesterone can bind to multiple receptors in the body, therefore this can have a substantial impact on the effects seen, particularly relation to hormonal changes and body composition.

Common forms of birth control include:

• Oral contraceptive (“The Pill”)
  • Two types:
    • Progestin only
    • Combination pill (estradiol + progestin) – Further classified as mono-, di-, or triphasic, which refers to the pattern of hormone levels over the month. 
• Depo-Provera injection (Progestin only)
  • An injection given into the muscle or under the skin providing birth control for up to 3 months.
• Merina (Progestin only)
  • A hormonal intrauterine device that can remain in place for approximately three years providing birth control throughout this time.
• Implanon (Progestin only)
  • Small rod placed in the upper arm providing a continuous hormone release for up to three years

Birth control and BMD

An area of particular interest among female athletes is the impact of birth control on BMD. Research investigating this area has produced mixed results often due to compliance issues and inconsistent testing of hormonal markers, however it is likely the effect of birth control on BMD depends on the type of birth control used. Some studies have shown the use of oral contraceptives may have positive effects on BMD for some female athletes, in particular those with pre-existing menstrual disturbances (3, 4). One study in particular showed the use of a low dose, monophasic, combined oral contraceptive produced a significant increase in BMD for oligo- and amenorrheic athletes after 10 months of treatment (5). The same results were not seen in sedentary controls. In contrast to this, several studies have found a common birth control method, Depo-Provera, may have a negative impact on BMD potentially by preventing the positive effect of exercise on BMD (6). However the results of these studies may be due to other factors such as inadequate calcium, other hormonal effects, or negative effects of synthetic progestin indicating the need for further research.

Of the available research, the use of combined oral contraceptives appears to have small effects on BMD for the regularly menstruating female that are unlikely to be of clinical significance. The best approach when deciding whether oral contraceptives are appropriate is based on the individual, considering both hormonal and lifestyle factors. Oral contraceptives may have beneficial effects on BMD, particularly in premenopausal women with oligo/amenorrhea (5). These women typically display a baseline BMD significantly lower than healthy controls (5). In such situations, if conservative measures are unsuccessful in assisting with the resumption of normal ovulatory menses in a reasonable time period, oral contraceptives may be an appropriate measure. It is important to note that oral contraceptives will not treat underlying hormonal issues, however they may prevent further BMD loss. Caution should be used when deciding if they are an appropriate measure. And if used, regular monitoring of BMD in conjunction with attention to external factors such as nutrition, training and lifestyle should be implemented. 

The main issues related to BMD arise with the use of progestin-only methods of contraception. While most appear to have minimal to no effect on BMD, the use of Depo-Provera has been shown to produce a hypo-estrogenic state in women as a result of the suppression of the hypothalamic-pituitary-ovarian axis without exogenous estrogen replacement, which could potentially cause a reduction in BMD (2). For women who have attained their peak bone mass, the use of Depo-Provera may cause BMD losses (6). And for females yet to obtain peak bone mass, Depo-Provera may impair the acquisition of peak bone mass (6). These findings are consistent among several studies, which show lower BMD in longer-term Depo-Provera users (3, 6, 7). With this being said, following cessation of use, BMD appears to increase again, irrespective of age, except for females who have reached menopause. Interestingly, higher body weight correlates with higher BMD, regardless of treatment with hormonal contraception, which suggests that both body weight and body fat could potentially override the negative effects of Depo-Provera (1).

Bone Stress Injuries

Bone stress injuries encompass both stress reactions and fractures. These injuries are an all too common occurrence among female athletes with menstrual irregularities and/or low BMD. The prevalence of stress fractures in athletic populations such as, track and field, and military recruits is 0.7% to 21%, with injuries of the foot and lower leg most common. That being said, any bone subjected to repetitive stress is at risk of bone related injuries  (1). Table 1 outlines stress injury risk factors. Athletes with amenorrhea are 2 to 4 times more likely to experience a stress fracture compared to eumenorrheic individuals (1). Additionally, the lower an individual’s BMD, the longer the recovery from a stress injury (1). Furthermore, the presence of other factors such low energy availability or disordered eating increases the risk of recurring injury.

Table1. Stress injury risk factors (1)

Prevention is the best treatment. Resumption of normal menses is a key goal of treatment in order to prevent further bone loss (8). Many athletes can be treated without the need for hormonal intervention, however in cases where osteoporosis is already present and/or there is a history of multiple fractures, hormonal intervention may be necessary. In most cases, estrogen is low, therefore estrogen treatment has been shown to have a beneficial effect on bone mass when prescribed via a transdermal route as opposed to oral (1). 

Improving energy availability is another key component of prevention of bone related injuries. By ensuring energy availability is sufficient, female athletes can avoid the suppression of reproductive and other important hormones critical to bone health. Low energy availability may result from “under fueling” or increased training load without a corresponding increase in energy intake. In most cases, addressing this mismatch in energy intake and expenditure can all but preserve the maintenance of bone health. 

Moreover, adequate intakes of calcium, vitamin D and vitamin K can foster bone health. For athletes, already having experienced a decline in bone health, there are currently no specific recommendations available.  The recommended intakes for athletes are outlined in Table 2. 

Table 2. Micronutrient requirements (9, 10, 11)

In summary

The consequences of poor bone health among female athletes, particularly those experiencing menstrual irregularities, is concerning and of grave importance. Not only should female athletes and coaches pay attention to bone health for athletic purposes, but more importantly for the female athletes health and maintenance of an active lifestyle over the lifespan. A lack of awareness among athletes, or in some cases a conscious decision to ignore the signs and symptoms of compromised bone health is problematic. This is what allows the silent process of bone loss to become all the more detrimental and costly. Finally, societal pressures and thin ideals  serve to add fuel to the fire, driving females to engage in extreme practices that thwart the preservation of their bone health. 

As with all health conditions, prevention is key. Yet despite the best of intentions and efforts by coaches and athletes, sometimes intervention is warranted. In such cases where bone health is at risk, it is in the best interests of the female athlete to begin addressing hormonal issues, prioritising adequate energy availability and ensuring they consume sufficient intakes of the previously mentioned vitamins and minerals. At the end of the day you only get one body, one skeleton. Look after them and they will serve you well.

References

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2. Fruth SJ, Worrell TW. Factors associated with menstrual irregularities and decreased bone mineral density in female athletes. J Orthop Sports Phys Ther. 1995, 22 (1): 26-39.
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4. Zeriun MF, T Malik, YM Ferede, et al. Changes in body weight and blood pressure among women using Depo-Provera injection in Northwest Ethiopia. BMC Res Notes. 2019, 512.

5. Rickenlund A, K Carlström, B Ekblom, et al. Effects of oral contraceptives on body composition and physical performance in female athletes. J Clin Endocrinol Metab. 2004, 89 (1): 4364-4370.

6. Spevack, E. The long-term health implications of Depo-Provera. J Evid-Based Integr Med. 2013, 12 (1): 27-34.

7. Meier C, YB Brauchli, SS Jick, et al. Use of Depot Medroxyprogesterone Acetate and fracture risk. J Clin Endocrinol Metab. 2010, 95 (11): 4909-4916.

8. Cobb KL, LK Bacrach, M Sowers, et al. The effect of oral contraceptives on bone mass and stress fractures in female runners. Med Sci Sports Exerc. 2007, 39 (9): 1464-1473.

9. Teegarden D, P Legowski, CW Gunther, et al. Dietary calcium intake protects women consuming oral contraceptives from spine and hip bone loss. J Clin Endocrinol Metab. 2005, 90 (9): 5127-5133.

10. Ogan D, K Pritchett. Vitamin D and the athlete: Risks, recommendations, and benefits. Nutrients. 2018, 5: 1856-1868.

11. Weber P. Vitamin K and bone health. Nutrition. 2001, 17 (10): 880-887.