Osteoporosis is a disease characterised by brittle bones, resulting in an increase in fracture risk. In the UK, 1 in 2 women and 1 in 5 men over the age of 50 suffer from osteoporotic fractures (National Osteoporosis Society, 2016) and this high prevalence causes a substantial cost to the National Health Service, writes Dr Jacky Forsyth – who works in the centre for Sport, Health and Exercise Research at Staffordshire University.
Osteoporosis is not limited to old age – deterioration in bone health can start at a young age due to inappropriate lifestyle choices – however, osteoporosis is generally not diagnosed until later in life. For this reason, osteoporosis has been described as a ‘silent disease’, in that an individual will not realise that they have it until they suffer from their first osteoporotic fracture, by which time, it is often too late to repair the damage already done.
Preventing the occurrence of osteoporosis, through changes in exercise and diet, is key to ensuing that this disease does not progress in our burgeoning ageing population. The role of the fitness professional in promoting positive lifestyle changes to improve people’s bone health is important in this prevention. The purpose of this article is to provide background information on bone remodelling and osteoporosis, and to suggest some novel, research-informed ideas that can be used to promote good bone health.
An individual is said to have osteoporosis if they have a T score, as measured using DXA (which stands for Dual-Energy X-Ray Absorptiometry) below -2.5, which means that their bone mineral density is 2.5 standard deviations below that of a healthy, young adult (World Health Organisation, 1994). A Fracture Risk Assessment Tool (FRAX®) has also been developed, which uses risk factors such as sex, age, family history of osteoporosis, and smoking status, to ascertain the likelihood of sustaining a fracture over a given period of time. Worldwide, an osteoporotic fracture is estimated to occur every three seconds (Jonell & Kanis, 2006), and as a result, wellbeing and quality of life can deteriorate (Forsyth & Babatunde, 2015). Determining risk of fracture by understanding the risk factors is the first step in preventing osteoporosis.
Bone is in a constant state of remodelling, whereby osteoclasts – which are the bone-absorbing cells – break down the bone leaving spaces, termed resorption pits. Osteoblasts – which are the bone-building cells – migrate towards these pits, secreting collagen and various proteins, to rebuild and re-mineralise the bone. This process is constantly happening in all parts of the bone, but at different stages, and takes approximately three months to complete (Forsyth & Davey, 2008).
Bone remodelling is determined by several factors, including the amount of calcium available in the blood, and the availability of hormones, such as oestrogen, growth hormone and testosterone. For instance, when blood calcium levels are low, bone is resorbed (breaks down), so that calcium stored within the bone is made available in the bloodstream. Conversely, when blood calcium levels are optimal (because of optimal levels of calcium intake), bone is built up. Oestrogen availability is a key factor for maintaining good bone health among women (Rosen, Bouillon, & Compston, 2013). When oestrogen levels are optimal, more bone builds up than is broken down. When oestrogen levels are low, there is increased bone resorption (breaking down) through increased osteoclastic activity.
Women’s oestrogen levels change throughout life. A natural drop in oestrogen occurs around the menopause. Low oestrogen levels can also occur among women using hormone-based contraception. Progesterone-only contraception, in particular Depot Medroxyprogesterone Acetate, also known as Depo Provera or ‘depo’, can be particularly devastating to bone, especially with sustained use, among adolescents, and with advancing age (Curtis & Martins, 2006). These contraceptives bring about changes in hormones similar to the change that occurs in the menopause. It is, therefore, important to ensure that the correct nutrition and exercise is undertaken to offset such reductions in oestrogen that occur throughout a female’s lifespan.
Most people believe that weight-bearing exercise is important for bone health. This is correct, but there are better exercises that can be done to specifically target the bone. Largely based on animal studies, bone responds to exercise that is dynamic, non-repetitive, and unusual (eg, Rubin, Sommerfeldt, Judex, & Qin, 2001). The duration of load and the number of repetitions are of minor importance. The best form of exercise to stimulate bone growth and health, especially for the lower body, is jumping (Babatunde, Forsyth, & Gidlow, 2012). The jumping should be of high intensity, but importantly, should be interspersed with short rest periods. In fact, in our research, we found that just 10 jumps on 3 days of the week, with each jump interspersed with a 10-second rest interval, was enough to improve bone health among premenopausal women, and was even sufficient for those women who were low in oestrogen, due to using hormone-based contraception (Babatunde & Forsyth, 2014). The jumps should be performed on a hard surface without protective footwear. To avoid injury, this activity should be progressed gradually, and should be discontinued if any musculoskeletal injuries arise.
Exercise for women with low levels of oestrogen, as a result of the menopause or because of hormone-based contraceptive use, has not always been found to be effective. For instance, heel drops, which involve raising the body onto the toes, then dropping onto the floor, were only found to be effective for improving the bone health of premenopausal women, not menopausal women (Bassey, Rothwell, Littlewood, & Pye, 1998). When exercise is combined with oral contraceptive use, bone health has been found to be lower than that of non-oral contraceptive users who do little exercise (Weaver et al., 2001). The lack of oestrogen may counteract the effect of exercise by inhibiting bone formation in response to the mechanical stress. In such situations, the exercise needs to be specifically targeted, by using, as just mentioned, the rest-inserted jumps.
To improve bone health in the upper body, our research team are currently investigating, through a systematic review, which exercises can be used to improve bone health of the wrist and forearm (Forsyth, Babatunde, Hind, & Paskins, 2017). It is likely that, similar to the lower body, exercise that is novel, of a high intensity, unique, and non-repetitive, will have the greatest effects. The usual moderate to high intensity exercise through cardiovascular work is not considered to be beneficial for bone health. Swimmers, for instance, have notoriously poor bone health, since there is limited impact in this sport. Cyclists and other athletes who engage in sport in which the body is supported, are also at risk.
Even running is not as beneficial for bone as other forms of exercise, since the body gets used to the repetitive loading and fails to continue to adapt. For instance, in a study of Masters runners (over 35 years old), sprinters were found to have better bone mineral density than that of long-distance runners (Gast et al., 2013). Weight training can be effective for bone health, but largely works by having an indirect effect – weight training builds muscle, which then pulls on the bone to cause increased bone turnover, and resultant increased bone health. Further research on the most effective exercise for the upper body is ongoing.
As well as calcium being important in the diet, with natural sources occurring in dairy products and dark green leafy vegetables, dried plums (prunes) have also been found to be effective in improving bone health. Prunes are polyphenol rich, with the particular combination of polyphenols targeting a decrease in bone resorption and hence an increase in bone health (Rendina et al., 2013). Prunes are also rich in boron, which stabilises and extends the half-life of vitamin D, improves oestrogen availability and use, and reduces calcium loss (Pizzorno, 2015). Adding 5-6 prunes per day to the diet can bring about substantial increases in bone health (Hooshman et al., 2011).
There are several additional lifestyle factors that are important for optimising bone health. Ensuring adequate amounts of vitamin D, through exposure to sunshine, is important. If an individual is covered up all the time, with clothing or with sun cream, or is predominantly indoors, vitamin D may become deficient. In a study in Sweden, it was recommended that 3 or more hours of sunlight were needed per day during the winter months, to ensure adequate vitamin D to maintain bone health (Melin, Wilske, Ringertz, & Sääf, 2001). Having a low body weight is a risk factor for osteoporosis. Body mass, whether in the form of muscle or fat, results in added mechanical load on bone during weight-bearing exercise and the bone adapts by becoming stronger. Having a body mass index of less than 19 kg/m2 is, therefore, associated with a greater risk of osteoporosis (Forsyth & Davey, 2008). For the exercising female, low body fat, due to low energy intake or due to excessive exercise, is often also associated with menstrual dysfunction, which further increases the risk of osteoporosis.
The novel, research-based findings reported here, such as the research on which exercise is most effective for improving bone health will be discussed in our book, coming out in 2018, ‘The exercising female’, published by Routledge, and will also form part of the content of our upcoming conference, Women in Sport and Exercise, Blood Sweat and Tears. The aim of the conference is to debate the female-specific health and medical issues arising from physical activity and sport, and to raise awareness of the issues and opportunities for women’s exercise participation. Other topics, in our book and conference, include: coping with the menstrual cycle; the effect of hormonal contraceptives; exercise in pregnancy; body image; exercise addiction; the female athlete triad; homophobia in sport; breast biomechanics, and the story behind the ‘This Girl Can’ campaign.
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