Lifetime body mass index and later atherosclerosis risk in young adults: examining causal links using Mendelian randomization in the Cardiovascular Risk in Young Finns study.
OBJECTIVE
Mendelian randomization uses genetic variants related to environmentally modifiable risk factors in an attempt to improve causal inference from observational data. We examined the effect of lifetime body mass index (BMI) on adult carotid intima-media thickness (CIMT) and various atherosclerotic risk factors by using both Mendelian randomization and conventional analyses.


RESULTS
A total of 2230 individuals (1218 women), aged 3-18 at study induction, took part in clinical examinations in 1980, 1983, 1986, and, most recently, 2001 when they were aged 24-39. In these analyses we utilized the known relation between FTO polymorphism rs9939609 and BMI. The dose-response association between the number of A alleles in FTO and higher mean BMI from childhood to adulthood was confirmed, but no associations with potential confounding factors were observed. In standard regression models, lifetime BMI was associated with adult CIMT, lifetime systolic blood pressure, adult fasting glucose, and adult HOMA-index. When variation in FTO was used as an instrument for unconfounded BMI levels, similar or larger effects of lifetime BMI on all these phenotypes were found, although with wider confidence intervals.


CONCLUSIONS
Mutually supportive results from Mendelian randomization and standard regression models strengthen the evidence of the effect of lifetime BMI on atherosclerosis risk in young adults.
Department of Epidemiology and Public Health, University College London, London, UK. m.kivimaki@ucl.ac.uk
Mika
M
Kivimäki
George Davey
GD
Smith
Nic J
NJ
Timpson
Debbie A
DA
Lawlor
G David
GD
Batty
Mika
M
Kähönen
Markus
M
Juonala
Tapani
T
Rönnemaa
Jorma S A
JS
Viikari
Terho
T
Lehtimäki
Olli T
OT
Raitakari
D000293:Adolescent; D000328:Adult; D000071516:Alpha-Ketoglutarate-Dependent Dioxygenase FTO; D050197:Atherosclerosis / Q000235:genetics* / Q000503:physiopathology; D001794:Blood Pressure / Q000235:genetics / Q000502:physiology; D015992:Body Mass Index; D017536:Carotid Artery, Common / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D015986:Confounding Factors, Epidemiologic; D004812:Epidemiologic Methods; D005260:Female; D005387:Finland; D014644:Genetic Variation / Q000235:genetics*; D005838:Genotype; D006801:Humans; D008297:Male; D010641:Phenotype; D011110:Polymorphism, Genetic; D011506:Proteins / Q000235:genetics*; D012959:Socioeconomic Factors; D017539:Tunica Intima / Q000473:pathology; D017540:Tunica Media / Q000473:pathology; D055815:Young Adult
D011506:Proteins; D000071516:Alpha-Ketoglutarate-Dependent Dioxygenase FTO; C526492:FTO protein, human