Influence of smoking and oral contraceptives on bone mineral density and bone remodeling in young women: a 2-year study

Abstract

The objective of the study was to explore the influence of menstrual irregularities, oral contraceptives and smoking on bone mineral density (BMD) development and bone turnover with time. Healthy young women (n = 118) were divided into four categories: (a) women neither smoking nor using oral contraceptives; (b) women who were smokers; (c) women using oral contraceptives; (d) women who were smoking and using oral contraceptives. They responded to a validated questionnaire with 34 questions concerning lifestyle and the Sense of Coherence scale (SOC). BMD was measured by dual energy x-ray absorptiometry (DEXA). Deoxypyridinoline (DPD) was measured in urine. Data were analyzed by multiple linear regression analysis. Among smokers, BMD level decreased during a 2-year period and smoking was associated with a larger negative change in BMD. Use of oral contraceptives moderated the negative impact of smoking. Women using oral contraceptives at baseline and with regular bleeding induced by contraceptive pills had a significantly higher BMD at baseline and at follow-up. They also had lower SOC than women who had natural regular bleedings. Use of oral contraceptives in combination with smoking was linked to high alcohol consumption and higher frequency of self-reported body weight reduction, which reduced the negative BMD change in this category. DPD level and difference were strongly associated with estrogen influence. It is concluded that smokers without OCs had a negative BMD development and BMD in young women with irregular menstruations seems to be improved by OC.

Introduction

Peak bone mass is determined by genetic factors [1], [2], [3] as well as hormonal [4] and lifestyle factors [5], [6]. Among healthy young women, the potential influence of smoking and use of oral contraceptives on development of bone mineral density (BMD) is not well understood, possibly due to covariation with other hormonal and lifestyle factors. Research on prevention has mainly focused on secondary prevention involving medical treatment strategies among postmenopausal women with or at risk of low BMD. Attainment of a high peak bone mass is considered a pivotal preventive strategy against future osteoporotic fractures [7]. In young women, primary prevention should focus on factors that influence peak bone mass. To provide information on both negative and positive lifestyle habits influencing the development of peak bone mass is of considerable importance in most societies.

Smoking is considered to have a negative impact on BMD, but among adolescents or young females there is a lack of data [8], [9]. Bone turnover rate as a predictor of bone gain in longitudinal studies on women [10], [11] is contradictory and seems to be dependent on pubertal stage. Among elderly women, aged 67–77, heavy smokers have an increased bone remodeling compared with nonsmokers [12]. Among young healthy males, no differences are seen in bone turnover markers between smokers and nonsmokers [13]. There is a lack of data about a possible association between bone turnover and smoking among young women and this must be investigated further. This knowledge could help to explain underlying factors complicating demonstration of an association between smoking and BMD in young women.

Smoking and use of oral contraceptives (OCs) seem to interact. Results from a population-based cohort study with prospectively collected 40 years of data on smoking showed that neither current smoking, lasting at least 10 years, nor early adulthood smoking, resulted in significantly lower BMD among women who had not taken estrogen [6]. As for smoking and intake of estrogen, BMD were lower but significance could not be found due to the small number of smokers [6]. The use of OCs has increased since women enrolled in the previous study and it seems important to delineate if women who smoke and use OCs have an increased risk of developing a low bone mass. Results from cross-sectional [14], [15] and prospective studies [16], [17] are to some extent conflicting as to whether use of OCs among young women exerts a positive influence on BMD. It has also been suggested that OCs in young women moderate bone turnover rate [18].

It is known that disturbances in menstrual cycles are associated with low BMD [19]. Long-term effects of stress due to the cumulative load of minor day-to-day stressors can have consequences on a person’s health [20] and prolonged stress could disturb the hormonal balance and, as a consequence, cause a disturbed menstrual pattern or irregular menstruation. How a person responds to potential stressful situations is determined by the way a person perceives a situation [21]. Also, the ability to adjust or habituate repeated stress is determined by how a person perceives stressful situations.

When examining the influence of exercise in combination with low-dose OCs on BMD in a population with regular menstruations, the highest BMD values were found in the group of women with long-term exercise and short-use of OCs [22]. In the group with long-term exercise and long-term intake of OCs, no such beneficial effects were found [22]. It has been suggested that OC intake could increase BMD among girls with disturbed menstrual cycles [23], [24]. However, combined contraceptive pills do not seem to improve BMD in menstruating women who are adequately estrogenized by their own ovaries [25]. In addition, there seems to be a covariation between OC and hormonal history that needs to be delineated and it can be assumed that lifestyle factors as well as menstrual history and pattern interact with smoking and use of OCs in influencing development of BMD.

The aim of this study was to explore a perceived influence of OCs and smoking among young women on BMD development and bone turnover over time. A further aim was to explore if history of menstrual irregularities in combination with use of OCs influence development of BMD.