Urban-Rural Differences in Bone Mineral Density: A Cross Sectional Analysis Based on the Hyderabad Indian Migration Study.
BACKGROUND
Fracture risk is rising in countries undergoing rapid rural to urban migration, but whether this reflects an adverse effect of urbanization on intrinsic bone strength, as reflected by bone mineral density (BMD), is currently unknown.


METHODS
Lumbar spine (LS) and total hip (TH) BMD, and total body fat and lean mass, were obtained from DXA scans performed in the Hyderabad arm of the Indian Migration Study (54% male, mean age 49 years). Sib-pair comparisons were performed between rural-urban migrants (RUM) and rural non-migrated (RNM) siblings (N = 185 sib-pairs).


RESULTS
In analyses adjusted for height, gender, age and occupation, rural to urban migration was associated with higher lumbar and hip BMD and greater predicted hip strength; ΔLS BMD 0.030 (0.005, 0.055) g/cm2, ΔTH BMD 0.044 (0.024; 0.064) g/cm2, Δcross-sectional moment of inertia 0.162 (0.036, 0.289) cm4. These differences were largely attenuated after adjusting for body composition, insulin levels and current lifestyle factors ie. years of smoking, alcohol consumption and moderate to vigorous physical activity. Further analyses suggested that differences in lean mass, and to a lesser extent fat mass, largely explained the BMD differences which we observed.


CONCLUSIONS
Rural to urban migration as an adult is associated with higher BMD and greater predicted hip strength, reflecting associated alterations in body composition. It remains to be seen how differences in BMD between migration groups will translate into fracture risk in becoming years.
Musculoskeletal Research Unit, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom; Children's Hospital, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland.
Heli T
HT
Viljakainen
School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
Yoav
Y
Ben-Shlomo
Department of Non Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom.
Sanjay
S
Kinra
Department of Non Communicable Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom; South Asia Network for Chronic Disease. Public Health Foundation of India, New Delhi, India.
Shah
S
Ebrahim
Department of Clinical Research, London School of Hygiene & Tropical Medicine, London, United Kingdom.
Hannah
H
Kuper
National Institute of Nutrition, Hyderabad, India.
K V
KV
Radhakrishna
National Institute of Nutrition, Hyderabad, India.
Bharati
B
Kulkarni
Musculoskeletal Research Unit, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom.
Jon H
JH
Tobias
D015502:Absorptiometry, Photon; D000328:Adult; D001823:Body Composition / Q000502:physiology; D015519:Bone Density / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging*; D050723:Fractures, Bone / Q000209:etiology*; D006801:Humans; D007194:India; D008019:Life Style; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment; D012424:Rural Population; D014505:Urban Population