Physical activity during the early years of life and osteoporosis in adulthood : study among users of the Brazilian National Health System

The objectives of this study were to analyze the association between osteoporosis and current/early physical activity and also to identify whether early sport participation, osteoporosis, age and sex are somehow connected. The study sample included 963 participants. Osteoporosis was diagnosed through medical records. Physical activity in current and the early years of life, age, sex and economic condition were assessed through questionnaires. Abdominal obesity was identified by waist circumference. Results showed that osteoporosis was associated with female sex and higher age. Participants that were active in adulthood had 47% lower chance of osteoporosis (odds ration [OR] = 0.53[0.30–0.93]). Adults that were active in childhood and adolescence had a lower chance of osteoporosis only in the crude model (OR = 0.38[0.22–0.64]). Women that were inactive in their youth were almost five times more likely to have osteoporosis when compared to men under the same conditions (OR = 4.80[2.46–9.37]). A lack of sports participation in the early years of life seems to be associated with osteoporosis, age and sex.


Introduction
In modern society, osteoporosis is a highly prevalent disease that constitutes a public health concern due to its significant impact on health care expenditure [1][2][3] .Older women are the most affected by this disease, making age and sex critical risk factors 1 .Recently, studies have reported an association between abdominal fat and bone mass density, suggesting that fat deposition in the central region of the body is harmful to bone health [4][5][6][7] .
In fact, the natural decrease in bone mass is a common process beginning at age 40, and it is exacerbated among females mainly due to hormonal, physical, and behavioral characteristics 8 .Regarding behavioral characteristics, women are less physically active than men from an early age 9 and exercise has been considered an important behavior related to the maintenance of bone health throughout life 10 .From a preventive point-of-view, physical inactivity in the early years of life has been associated as being harmful to health in adulthood, a crucial period of life for the development of several non-communicable diseases 9,11 .Childhood and adolescence are stages of the human development during which the bone mass is determined and, therefore, sports participation during these periods could improve bone mass accrual and, hence, prevent osteoporosis in adulthood 12,13 .In addition, scientific literature indicates that children and adolescents that are physically active tend to remain active throughout adulthood 14,15 .
Conversely, the impact of physical activity in the early years of life on osteoporosis in adulthood is not clear and it is not known if physical activity performed in the early years of life can be associated with osteoporosis, age, and sex.Thus, the purposes of this study were (i) to analyze the association between osteoporosis and current/early physical activity and also (ii) to identify whether early sport participation, osteoporosis, age, and sex are somehow associated.

Sample
The study was carried out from August to December 2010 in __________, a medium-sized (~360,000 inhabitants) city in

Outcome: Osteoporosis
The occurrence of osteoporosis was based on physician diagnosis identified through medical records of the participants.

Independent variables: Current physical exercise and sports activities in childhood and adolescence
Information concerning habitual exercise was assessed using the second section of the questionnaire developed by Baecke and colleagues 17 .We analyzed three aspects of exercise/ sports participation: i) intensity (low, moderate or vigorous), ii) minutes per week (< 60 minutes/week; 60-120 minutes/ week; 120-180 minutes/week; 180-240 minutes/week; > 240 minutes/week), and iii) previous time engaged (<1 month, 1-3 months, 4-6 months, 7-9 months, > 9 months).Participants were considered sufficiently active when they reported at least 180 minutes of exercise/sports per week (180-240 minutes/ week) on moderate or vigorous intensity over the last four months (4-6 months).
Early sports participation was analyzed using two questions 9,14,18 : (i) "Outside school, were you ever engaged in any organized/supervised sport activities for at least one year from age 7 to 10 years old?" and (ii) "Outside school, were you ever engaged in any organized/supervised sport activities for at least one year from age 11 to 17 years old?" Adequate levels of reproducibility for early sport participation have been previously reported 9 .For statistical analyses, a variable was created with three possible categories: (i) None: if the participant responded "no" to both questions; (ii) One period: if the participant responded "yes" to just one question; and (iii) Two periods: if the participant responded "yes" to both questions 9 .

Potential confounders
The following data were used as potential confounders: (i) socio-demographic variables (sex, chronological age [structured as a categorical variable: <65 years old and ≥65 years old]); (ii) abdominal obesity, identified by waist circumference measurements (cut-off point for women, 88 cm; men, 102 cm) 19,20 ; (iii) economic status, assessed by a specific and previously validated Brazilian questionnaire 21 , which estimates the family income (dichotomized into low or high income).

Statistical analysis
Categorical data were expressed as rates and 95%CI.Chi-square test (χ 2 ) analyzed the existence of association (Yates' correction was applied in 2 × 2 contingency tables) and binary logistic regression (presented as values of odds ratio [OR] and its 95% confidence intervals [95%CI]) indicated the magnitude of these associations.Spearman correlation was used to assess the relationship between dependent and independent variables.Statistical procedures were performed using the software BioEstat (release 5.0) and all statistical analyses were set at p < 0.05.

Results
The age of the sample population ranged from 50 to 96 years (mean 64.7 years).Analyzing the occurrence of osteoporosis with risk factors, the crude model showed association between osteoporosis and female sex (OR = 5.22 [  1).
Regarding current physical activity, adults that were engaged in at least 180 minutes of physical activity per week had 47% less chance of osteoporosis compared to inactive participants, even after adjustments for sex and age (OR = 0.53 [0.30-0.93])(Table 2).Concerning sports participation in the early years of life, adults that were active in childhood and adolescence had a lower likelihood of osteoporosis only in the crude model (OR = 0.38 [0.22-0.64])(Table 2).When analyzing the interaction of osteoporosis with physical activity in the early years of life and sex, women that were inactive during their youth were almost five times more likely to have osteoporosis when compared to men under the same conditions, even after adjustments for age and current physical activity (OR = 4.80 [2.46-9.37])(Table 3).
Finally, we found correlations between osteoporosis and age only among adults who were inactive in the early years of life (r = 0.133 [0.065 to 0.199]) (Table 4).

Discussion
In this cross-sectional study with adult users of the Brazilian National Health System, it was possible to identify that the occurrence of osteoporosis was higher in women and older people, mainly when there was absence of sport participation in the early years of life.
Age and sex were significantly associated with osteoporosis, confirming previous position statements of the North American Menopause Society 22 and the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis 23 .In fact, aging modifications are associated with decreased lean body mass, increased fat [24][25][26] and, in women, due to menopause, a noticeable reduction or absence of hormones also contribute to bone loss [27][28][29] .
Higher economic status was also associated with lower occurrence of osteoporosis in our sample.Actually, the role that economic status plays in people's risk for osteoporosis has not been well understood.Trying to explore this association, a recent study conducted in Spain found that lower economic status was linked to higher parathyroid hormone, higher bodyweight, higher body mass index, vitamin D insufficiency, lower body mass index at the lumbar spine, and a higher prevalence of vertebral and non-vertebral fracture 30 .In Brazil, Martini and colleagues 31 investigated 54,369 individuals in Brazilian capitals and concluded that higher levels of education provided protection for the occurrence of osteoporosis.In another Brazilian study with women, 73.3% reported having osteoporosis and/or osteopenia and were considered illiterate 32 .
Concerning the association between osteoporosis and abdominal obesity, previous studies reported negative relationships between measurements of abdominal obesity and lower bone mass 33,34 .The pathways by which abdominal obesity affects bone tissue are not completely understood yet, but involve the action of inflammatory markers produced by adipose tissues, which affect the osteoblasts/osteoclasts ratio in the bone matrix 35 , leading to lower bone mass.
In regards to lifestyle factors, current physical activity was associated with lower occurrence of osteoporosis, findings similar to those of other studies 16,36 .When analyzing physical activity performed during the early years of life, our results indicated that women who were inactive in childhood and adolescence were almost five times more likely to have osteoporosis when compared to men under the same conditions, even after adjustments for age and current physical activity.These results indicate that lack of sports participation in the early years of life is associated with osteoporosis, age, and sex.According to Lima and colleagues 12 , sport activity performed during childhood/adolescence was related to higher bone mineral density, even after adjustments for current physical activity, obesity and other variables harmful to bone formation.These findings show that current physical activity could act as a support factor in reducing bone loss caused by the aging process, but, in fact, bone mass is determined during childhood/adolescence.From this perspective, this finding highlights the importance of sports participation during childhood/adolescence in preventing outcomes such as osteoporosis in adulthood 12 .
However, limitations should be recognized: the cross-sectional design constitutes the main limitation due to non-possibility of causality statements.Therefore, prospective studies analyzing this issue in participants of the public healthcare system are necessary.Moreover, the absence of measures of bone mineral content, density, and methylation rates should be recognized as significant limitations.We also recognize the lack of information about intensity of sports activities in childhood and adolescence.
In summary, we conclude, in this representative sample of adult users of the Brazilian National Health System, that lack of sports participation in the early years of life is associated with osteoporosis, age, and sex. 6able 4. Partial and bivariate correlations between osteoporosis and age according to early sport participation (n = 963).Notes: 95%CI = 95% confidence interval; Model-1 = crude; Model-2 = controlled by current physical activity; Model-3 = controlled by sex; Model-4 = controlled by sex and current physical activity.

Physical activity during the early years of life and osteoporosis in adulthood: study among users of the Brazilian National Health System
_______, the richest state in ______.Public primary health care in the city consists of 17 basic health care units.Sample size estimation identified the necessity of interviewing at least Turi B.C. & Codogno J.S. & Lynch K.R. & Araújo L.G.M. & Locci B. & Monteiro H.l.

Table 1 .
Associations between osteoporosis and some independent variables among Brazilian adults (n = 963).

Table 2 .
Associations between osteoporosis and early/current physical activity among Brazilian adults (n = 963) Notes: OR = odds ratio; 95%CI = 95% confidence interval; PA = physical activity; *, multivariate model simultaneously adjusted by sex and age.

Table 3 .
Associations between osteoporosis and sex according to sport participation in childhood and/or adolescence (n = 963).