Physiological factors associated with low bone mineral density in female endurance runners

Abstract

Objective: To explore potential factors that could be associated with low bone mineral density (BMD) in female endurance runners. Methods: Fifty two female endurance runners (1500 m to marathon), aged 18-44 years, took part. Body fat percentage, lumbar spine BMD, and femoral neck BMD were measured using the Hologic QDR 4500w bone densitometer. Data on training, menstrual cycle status, osteoporosis, and health related factors were obtained by questionnaire. Dietary variables were assessed from a prospective seven day dietary record of macronutrients and micronutrients. Results: The mean (SD) lumbar spine and femoral neck BMD were 1.11 (0.11) and 0.89 (0.12) g/cm 2 respectively. A backward elimination regression analysis showed that age, body mass, body fat, distance run, magnesium, and zinc intake were the variables significantly associated with BMD. Lumbar spine BMD (g/cm 2 ) = −1.90 + (0.0486 × age (years)) + (0.342 × log mass (kg)) − (0.000861 × age 2 (years)) − (0.00128 × distance (km/week)), with an R 2 = 30.1% (SEE = 0.089 (95% confidence interval (CI) 0.05 to 0.23); p<0.001). Femoral neck BMD (g/cm 2 ) = −2.51 − (0.00989 × age (years)) + (0.720 × log mass (kg)) + (0.000951 × magnesium (mg/day)) −(0.0289 × zinc (mg/day)) − (0.00821 × body fat (%)) − (0.00226 × distance (km/week)), with an R 2 = 50.2% (SEE = 0.100 (95% CI 0.06 to 0.22); p<0.001). The negative association between skeletal BMD and distance run suggested that participants who ran longer distances had a lower BMD of the lumbar spine and femoral neck. Further, the results indicated a positive association between body mass and BMD, and a negative association between body fat and BMD. Conclusions: The results suggest a negative association between endurance running distance and lumbar spine and femoral neck BMD, with a positive association between body mass and femoral neck and lumbar spine BMD. However, longitudinal studies are required to assess directly the effect of endurance running and body mass on BMD, and to see if the addition of alternative exercise that would increase lean body mass would have a positive effect on BMD and therefore help to prevent osteoporosis.

Efeitos da atividade física na densidade mineral óssea e na remodelação do tecido ósseo

“…Although the level of the physical activity is a positively related variable to high BMD values, according to Gremion et al (24) , the high output endurance training might lead to an early bone loss due to the effects of the sexual female hormones on the homeostasis, and a consequent secondary amenorrhea, whose clinical picture is characterized by a decreasing number of menstrual cycles (6) . Such effect is similar to what happens in postmenopausal women, whose low concentration of the sexual hormones implies in an accentuated bone loss and the consequent osteoporosis (5,7) .…”

“…Those substances have been used as biochemical markers for the bone remodeling, and its concentrations have been measured in athletes or individuals submitted to some method of physical training to assess an eventual effect on the bone remodeling (6,7,17,18) .…”

“…In general, the same studies have shown positive results related to the BMD (8,15,(17)(18)(19)(20)(21)(22)(23) . Nevertheless, despite this possible benefic effect, quite large training volumes may cause a damage on the BMD, and it seems that such damage is closely related to the disturbance in the hormonal homeostasis of the organism (5,6,24) .…”

“…Although the majority of studies emphasize the effect of the type of the physical exercise on the BMD, other factors seem to interfere in that variable as well, such as the muscular strength (25) and the body composition (6,19,26) . In this perspective, regardless the level of the physical activity, some studies have shown that BMD in physically active output athletes or even the sedentary ones seem to pursue an association to their muscular strength developed according to the type of the physical exercise or daily activity, and their body composition (6,19,25,26) . Based on the aspects approached in the above mentioned studies, the aim of this article is to make a review on the effects of different sportive modalities and the strength training on the bone health, and also to analyze its possible benefic or harmful mechanism.…”

“…The maintenance of the BMD is very important to prevent the osteoporosis, which is characterized by an accentuated decrease in the BMD (3) , in which the bone matrix and minerals are lost due to an excessive bone reabsorption that is related to its formation (4) . This process is normally associated to the aging process and is an occurrence derived from the menopause (5) that leads to a higher incidence for fractures (6) . Although the bone loss is more intense in women (5,7) , men also present a decrease caused by the advanced age (8) .…”