Physical activity and bone mineral density in postmenopausal women without estrogen deficiency in menstrual history

© 2013 Amila Kapetanoviæ, Dijana Avdiæ; licensee University of Sarajevo Faculty of Health Studies. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. UNIVERSITY OF SARAJEVO FACULTY OF HEALTH STUDIES ABSTRACT


INTRODUCTION
Osteoporosis is characterized by low bone mass which may be the consequence of development of the skeleton during adolescence (low "peak" bone mass) and/or exessive bone loss thereafter (1).Sex hormones are crucial for keeping bone mass in balance, and the lack of either estrogen or testosterone leads to decreased bone mass and increased risk for osteoporosis (2).After menopause phase of accelerated bone degradation occurs and lasts 4-8 years, initiated by dramatic reduction in estrogen production by the ovaries (3,4).
Both estrogen and androgens inhibit bone resorption via eff ects on the receptor activator of NF-kap-paB ligand RANKL/RANK/osteoprotegerin system, as well as by reducing the production of a number of pro-resorptive cytokines, along with direct eff ects on osteoclast activity and lifespan (5).Estrogens and androgens also exert eff ects on the lifespan of mature bone cells: pro-apoptotic eff ects on osteoclasts but anti-apoptotic eff ects on osteoblasts and osteocytes (6).Sex steroid eff ects on bone formation are also likely mediated by multiple mechanisms, including a prolongation of osteoblast lifespan via non-genotropic mechanisms, as well as eff ects on osteoblast diff erentiation and function (5).Estrogen is known to have a variety of eff ects on the proliferation and synthesis of enzymes and bone matrix proteins by osteoblast -like cells through a process mediated by complex biomolecular biologic signals and mechanisms (7).Th e activities of osteoblasts and osteoclasts are controlled by a variety of hormones and cytokines, as well as by mechanical loading (2).Biochemical and molecular biological studies have resulted in the identifi cation of the gene of which expression level is changed by mechanical stress (8).Bone tissue has a mechanosensing apparatus that directs osteogenesis to where it is most needed to increase bone strength and the most likely sensors of mechanical loading are the osteocytes, which are visco-elastically coupled to the bone matrix so that their biological response increases with loading rate; thus, increasing loading frequency improves the responsiveness of bone to loading (9).Research shows that physical activity modifi es level of various hormones involved in bone metabolism, including gonadal sex hormone levels and calciotropic hormone levels (10,11,12).Th e reproductive abnormalities observed in female athletes generally originate in hypothalamic dysfunction and disturbance of the gonadotropin-releasing hormone (GnRH) pulse generator, although specifi c mechanisms triggering reproductive dysfunction may vary across athletic disciplines, the clinical consequences associated with suppression of GnRH include infertility and compromised bone density, which appears to be irreversible (13).Th e aim of this study was to examine infl uence of physical activity on bone mineral density in postmenopausal women without estrogen defi ciency in their menstrual history (no late menarche, no premature menopause).

METHODS
Th is prospective study included 100 postmenopausal women living in Sarajevo area (Sarajevo Canton) without estrogen defi ciency in menstrual history (normal menstrual history).Mineral bone density was measured at the lumbar spine and proximal femur by Dual-Energy X-ray Absorptiometry using Hologic QDR-4000 scanner.Examination group included 50 postmenopausal women, ages between 50 and 65, with osteoporosis (a value of BMD 2.5 standard deviations or more below the young adult mean) Control group included 50 postmenopausal women, ages between 50 and 65, with osteopenia (a value of BMD more than 1 standard deviations below the young adult mean, but less than 2.5 standard deviations below this value) or normal bone mineral density (a value of BMD within 1 standard deviation of the young adult reference mean) Th e women in the both group had normal menstrual history, without estrogen defi ciency in menstrual history (no late menarche, no premature menopause).Th e inclusion criteria were: women aged 50-65 years, women who live in the Sarajevo Canton, postmenopausal women without estrogen defi ciency in menstrual history (no late menarche, no premature menopause), women who do not use hormone replacement therapy, women whose fi nding's of bone densitometry (DEXA) was at the level of osteoporosis, women whose fi nding's of bone densitometry (DEXA) was at the level of osteopenia or normal.Th e exclusion criteria were: women younger than 50 and older than 65 years, women who do not live in the Sarajevo Canton, postmenopausal women with estrogen defi ciency in menstrual history (late menarche, premature menopause), women who are not postmenopausal, women who use hormone replacement therapy, women who have a disease that can cause osteoporosis, women who use medicines that may cause osteoporosis.
To assess level of physical activity an International Physical Activity Questionnaire -Long Form (IPAQ -Long Form), was used.Physical activity was assessed in the four domains: work-related physical activity, transport-related physical activity, domestic and gardening (yard) activities and leisure time physical activity, in the last 7 days.Th ere are three levels of physical activity (categorical score): low physical activity, moderate physical activity and high physical activity.Mentioned are only those activities which were carried out for at least 10 minutes.

Statistical analysis
Statistical signifi cance between examination and control group in physical activity level was tested by Chi square test.P < 0.05 was considered statistically signifi cant.

RESULTS
Th e average age of women without estrogen deficiency in their menstrual history in the examination group was 58.64 years, and in the control group was 57.9 years.Th ere was no statistically signifi cant differences between these two groups, t = 0.746.In the examination group of women who had no history of menstrual estrogen defi cit, level of physical activity was low in 26 (52.00%) female, and in 24 (48%) women level of physical activity was moderate.In the control group of women who had no history of menstrual estrogen defi cit in 5 (10.00%) female level of physical activity was low, and in 45 (90.00%) female level of physical activity was moderate.Th e diff erence in levels of physical activity between the two groups was statistically signifi cant, X² test = 20.6,p <0.005.osteoporosis induced by estrogen defi ciency has emerged as the most widely spread bone/joint disease in developed countries (14).Loss of estrogen leads to increased rate of remodeling and tilts the balance between bone resorption and formation in favor of the former (6).Post-menopausal osteoporosis is characterized by increased fracture risk due to defi ciencies in both the quantity and quality of bone (15).Th e aim of this study was to examine infl uence of physical activity on bone mineral density in postmenopausal women who hadn't a defi cit of estrogen in their menstrual history (no late menarche, no premature menopause).Th e mechanisms through which physical activity aff ects the bone tissue are incompletely understood, and some results of research are contradictory (16).Model of the osteogenic potential of exercise has not been established in humans (17).Research suggest that the frequency, intensity, time and type of physical activity, is directly related to its eff ects on bone tissue.

Among the estrogen target organs, bone has recently drawn increasing attention because postmenopausal
In the study of Bonaiuti D et al. showed that aerobics, weight bearing and resistance exercises are all eff ective in increasing the BMD of the spine in postmenopausal women, and walking is also eff ective on the hip (18).Hagberg JM. et al. fi nd that prolonged low-to-moderate-intensity physical activity, but not the same number of years of higher-intensity training for competitive events, was independently associated with higher BMD (19).(24).Ethnic diff erences in absolute fracture risk may warrant ethnic-specifi c clinical recommendations (25).Th ere is a large variation in hip fracture incidence from diff erent regions of the world (26).Bone loss subsequently occurs with ageing in both sexes, and in females accelerated loss occurs at the menopause (27).Due to these variations it is necessary that research be carried out within certain population groups.In this study, investigated was the infl uence of physical activity on bone mineral density in postmenopausal women, aged 50-65 years, who live in the area of Sarajevo Canton, who did not have a defi cit of estrogen in their menstrual history (no late menarche, no premature menopause).Physical activity in daily life was examined in the four domains: work-related physical activity, transport-related physical activity, domestic and gardening (yard) activities and leisure time physical activity.Th ere were three levels of physical activity (categorical score): low physical activity, moderate physical activity and high physical activity.It was shown that moderate intensity physical activity, performed during daily life, positively aff ects bone mineral density.
Based on the results of the research, physical activity of moderate intensity is recommended in the course of daily life, in order to maintain and improve bone health in postmenopausal women (menstrual history without estrogen defi ciency), aged 50-65 years, who live in the area of Sarajevo Canton.

CONCLUSION
Results of this study suggest that moderate physical activity has positive impact on bone mineral density in postmenopausal women (without estrogen deficiency in menstrual history) and has the potential to reduce rapid bone loss associated with decrease in estrogen at the time of menopause.