Impact on weight dynamics and general growth of the common FTO rs9939609: a longitudinal Danish cohort study

OBJECTIVE AND DESIGN

We investigated the impact of the fatness-related FTO rs9939609 A-allele on cross-sectional and longitudinal measures of body mass index (BMI), height and lean body mass (LBM) in a unique cohort representing a broad range of BMI.

SUBJECTS AND MEASUREMENTS

A random sample of all men attending the Danish draft boards during 1943-1977 plus all men with a BMI>or=31.0 kg/m(2) (assuring representation of the right end of the distribution) was taken. Anthropometric measures were available at up to eight points in time from birth to adulthood in 1629 genotyped men. The odds ratio (OR) for being a carrier of FTO rs9939609 according to (1) one unit alteration in z-scores for BMI, height and LBM at given ages and (2) longitudinal changes in BMI and height z-scores were assessed by logistic regression.

RESULTS

Except at birth, the AA genotype was associated with increased BMI z-scores at all point during the monitored lifespan, starting at the age of 7 years. This effect remained stable until early adulthood, where further weight gain occurred. The AA genotype was also--mainly through the effect on fatness--associated with accelerated linear growth in childhood (age 7 years; OR, 1.36; 95% confidence interval (CI), 1.06-1.74) and increased LBM in adulthood (OR, 1.24; 95% CI, 1.14-1.35).

CONCLUSION

Fatness induced by FTO rs9939609 in early childhood is sustained until early adulthood, where further weight gain may occur. FTO rs9939609 may, however, also be associated with linear growth and LBM mainly through the effect on fat mass.

Lack of association of fatness-related FTO gene variants with energy expenditure or physical activity

CONTEXT

A common variant in the first intron of FTO (rs9939609, T/A) is associated with fatness in Caucasians.

OBJECTIVE

FTO may regulate energy homeostasis through the hypothalamus, and we hypothesized that AA-genotypes of rs9939609 FTO have lower energy expenditure and/or a lower level of physical activity.

METHODS

The study population included all obese young men (body mass index > or = 31 kg/m(2)) at the mandatory draft board examinations in the Copenhagen area from 1943 to 1977 and a randomly selected control group from this population. Subgroups of 234 obese and 323 controls were examined in 1998-2000 (median age 48 yr). Fat mass (FM), lean body mass (LBM), leisure-time physical activity (LTPA), maximum oxygen uptake (VO(2)max), resting energy expenditure (REE), and glucose-induced thermogenesis (GIT) were measured. The FTO rs9939609 variant was genotyped. A recessive transmission mode fit the data best. Logistic regression was used to assess the odds ratios of the AA-genotype in relation to LTPA, VO(2)max, REE, and GIT.

RESULTS

The AA-genotype of FTO rs9939609 had higher REE in the age-adjusted model, but the association was eliminated when adjusting for FM and LBM. The AA-genotype was not associated with LTPA, VO(2)max, or GIT. This was not influenced by adjustment for age, FM, or LBM. The AA-genotype had increased FM, even with adjustment for age, LBM, REE, GIT, VO(2)max, and LTPA. Results were similar for FTO rs8050136 and rs7193144.

CONCLUSIONS

Homozygous carriers of the A-allele of rs9939609 FTO do not have lower REE, GIT, VO(2)max, or LTPA but higher FM, irrespective of LBM, REE, GIT, VO(2)max, and LTPA.

Does the relationship between waist circumference, morbidity and mortality depend on measurement protocol for waist circumference?

There is currently no consensus regarding the optimal protocol for measurement of waist circumference (WC), and no scientific rationale is provided for any of the WC protocols recommended by leading health authorities. A panel of experts conducted a systematic review of 120 studies (236 samples) to determine whether measurement protocol influenced the relationship of WC with morbidity of cardiovascular disease (CVD) and diabetes and with mortality from all causes and from CVD. Statistically significant associations with WC were reported for 65% (152) of the samples across all outcomes combined. Common WC protocols performed measurement at the minimal waist (33%), midpoint (26%) and umbilicus (27%). Non-significant associations were reported for 27% (64) of the samples. Most of these protocols measured WC at the midpoint (36%), umbilicus (28%) or minimal waist (25%). Significant associations were observed for 17 of the remaining 20 samples, but these were not significant when adjustment was made for covariates. For these samples, the most common WC protocols were the midpoint (35%) and umbilicus (30%). Similar patterns of association between the outcomes and all WC protocols were observed across sample size, sex, age, race and ethnicity. Our findings suggest that WC measurement protocol has no substantial influence on the association between WC, all-cause and CVD mortality, CVD and diabetes.

Abdominal Obesity and Fatty Liver

It has been hypothesized that visceral fat releases free fatty acids and adipokines and thereby exposes the liver to fat accumulation. The authors aimed to evaluate current epidemiologic evidence for an association between abdominal fat and liver fat content. Clinical and epidemiologic studies with data on abdominal fat and liver fat content were reviewed. Studies using waist circumference to estimate abdominal fat mass suggested a direct association between abdominal fat and liver fat content. Studies using imaging methods suggested a direct association between intraabdominal fat and liver fat content, but not between subcutaneous abdominal fat and liver fat content. In conclusion, clinical and epidemiologic studies of abdominal fat and liver fat content suggest a direct association between abdominal fat and liver fat content which is probably accounted for by visceral fat. However, results from the included studies do not allow strong conclusions regarding the temporal sequence of events. Future longitudinal studies are recommended to obtain additional information on associations and mechanisms. Both abdominal fat depots and other body compartments of interest should be included to further investigate the association between specific fat depots and liver fat content. Biomarkers may provide insight into underlying mechanisms.

Long-term effects of leisure time physical activity on risk of insulin resistance and impaired glucose tolerance, allowing for body weight history, in Danish men

AIMS

To determine if the level of leisure time physical activity (LTPA) in young adulthood in obese and non-obese men reduces the risk of insulin resistance (IR) and impaired glucose tolerance (IGT) in middle age, and if such an effect is explained by the current level of LTPA, or by the body mass index (BMI) history preceding and subsequent to the assessment of LTPA.

METHODS

Longitudinal study of groups of obese and randomly selected non-obese men identified at around age 19, and re-examined at mean ages of 32, 44 and 51. BMI was measured at all four examinations. LTPA was assessed by self-administrated questionnaires at the last three examinations. IR and the presence of IGT was determined by an oral glucose tolerance test at the last examination.

RESULTS

LTPA in young adulthood reduced the risk of IR and IGT in middle age throughout the range of BMI. Adjustment for the BMI history preceding and subsequent to the assessment of LTPA attenuated the association with IR and IGT, but active men remained at low risk of IR and IGT. Adjustment for subsequent and current levels of LTPA, smoking habits, alcohol intake, educational level and family history of diabetes had no notable influence on the results.

CONCLUSION

LTPA appears to reduce the risk of IR and IGT, an effect which is not explained by the current level of physical activity, and only partially explained by the BMI history preceding and subsequent to the assessment of LTPA.

Interactions between physical activity and variants of the genes encoding uncoupling proteins −2 and −3 in relation to body weight changes during a 10-y follow-up

OBJECTIVE

To examine interactions between physical activity and possibly functional variants of the genes encoding uncoupling proteins -2 and -3 in relation to body weight change. We hypothesize that physical inactivity acts synergistically with a 45 bp insertion variant in the 3'untranslated region (3'UTR) of the UCP2-gene and with a t-allele of codon -55 in the promoter of the UCP3-gene in relation to subsequent weight change.

DESIGN

Population-based longitudinal study of cohorts of juvenile obese and nonobese men, who were identified at the mandatory draft board examination in Copenhagen and adjacent regions at a median age of 19 y in 1943-77 and later examined at general health surveys in 1981-83 and 1991-93. The juvenile obese cohort included 568 men who at the draft board had a BMI > or =31 kg/m2 and the cohort of controls included 717 randomly selected draftees.

MEASUREMENTS

Height and weight were measured, and information about physical activity was collected from a self-administered questionnaire. The genotyping of the polymorphisms was performed using RFLP techniques. The main outcome measure was change in BMI during the 10-y follow-up period. Additional outcome measures were obesity, waist circumference and body fat mass index measured at follow-up.

RESULTS

Physical activity, the 3'UTR insertion polymorphism and the -55 c/t polymorphism were not consistently associated with changes in BMI, and there were no evidence for interactions between the UCP-variants and physical activity in relation to changes in BMI. No evidence for interaction between the UCP-variants and physical activity was found in relation to the additional obesity measures.

CONCLUSION

This study does not support that interactions between physical activity and variants in the UCP2- or UCP3-gene are major determinants of subsequent weight changes in Danish Caucasian men.