Low lumbar spine bone mineral density in both male and female endurance runners

Abstract

There have been many reports of low bone mineral density (BMD) in female endurance runners. Although there have been several reports of low BMD in male runners, it is unclear how comparable the problem is to that in females. We compared BMD between male and female endurance runners and with a reference population. One hundred and nine endurance runners (65 females, 44 males) aged 19–50 years participated and had been training regularly for at least 3 years (32–187.2 km week⁻¹) in events from 3 km to the marathon. BMD was measured at the lumbar spine (L2–L4) and hip by DXA. A questionnaire assessed training and menstrual status. Lumbar spine T scores were similar in male and female runners (−0.8 (0.8) versus −0.8 (0.7); f = 0.015; P = 0.904) as were total hip T scores (0.6 (7.9) versus 0.5 (9.2); f = 0.192; P = 0.662). The proportion of male runners with low lumbar spine BMD (<−1.0) (n = 16 from 44) compared to that of females (n = 27 from 65) (P = 0.675). Males had lower spine T scores than eumenorrhoeic females (−0.8 (0.7) versus −0.4 (0.7); f = 5.169; P = 0.03). There were moderate negative correlations between weekly running distance and lumbar spine BMD in males and females (r² = 0.267; 0.189; P < 0.001), independent of menstrual status in females (r² = 0.192; P < 0.001). Lumbar spine but not hip T scores were greater in runners who participated in resistance training at least twice-a-week (male: −0.4 versus −1.1; female: −0.5 versus −1.1; P < 0.01). Using multiple regression, running distance (−) and BMI (+) together best predicted lumbar spine T scores (r² = 0.402; P < 0.01) in females. Although weak, BMI (+) best predicted hip T scores (r² = 0.167; P < 0.05). In males, running distance and training years (−) together best predicted lumbar spine T scores (r² = 0.400; P < 0.01). Training years (−) best predicted hip T scores (r² = 0.361; P < 0.01). To conclude, our findings suggest that male runners face the same bone threat at the spine, as female runners. Further research in male athletes is required. Incorporation of regular resistance training into an athlete's training programme may be a useful preventative strategy.

Introduction

Since the early 1980s, many studies have confirmed the problem of low bone mineral density (BMD) in highly trained female athletes, particularly in endurance runners, and this evidence continues to accumulate. Cross-sectional studies report between 3 and 24% lower BMD in highly trained female runners compared to age-matched controls [1], [2], [3], [4] and longitudinal studies report significant bone loss over 2 to 10 years in female runners [5], [6]. There is some evidence for low BMD in male runners [7], [8], [9], [10], [11], although this has received relatively little attention, despite the recognition that 1 in 5 men will suffer from osteoporosis in their lifetime [12].

Suggested risk factors for low BMD in female athletes include exercise-induced amenorrhea (absence of menses), disordered eating and low body weight. Although estrogen deficiency was once presumed the underlying cause [1], [2], [3], [4], [5], [6], [13], it is now established that energy deficiency (arising from disordered eating or simply an insufficient energy intake to match expenditure [14], [15]), is the driving factor for bone loss and low BMD in this population [16]. Of interest, animal studies indicate that exercise-induced menstrual irregularity and the associated estrogen deficiency are secondary to energy deficit [17]. In male runners, low BMD appears to be unrelated to levels of sex hormones [8], [9], [10], but short-term energy deficiency has been shown to suppress bone formation in male athletes [18].

To date, no studies have compared BMD in male and female runners; thus, the hypothesis that low BMD in athletes should only be of significant concern for females has not yet been tested. In light of this, we aimed to compare BMD between male and female runners and with a reference population. This would seem an important starting point from which further studies can investigate potential factors associated with BMD in athletes, which may or may not be sex-specific.