Trends in childhood body mass index between 1936 and 2011 showed that underweight remained more common than obesity among 398 970 Danish school children

AIM

To examine trends in all body mass index (BMI) groups in children from 1936 to 2011.

METHODS

We included 197 694 girls and 201 276 boys from the Copenhagen School Health Records Register, born between 1930 and 1996, with longitudinal weight and height measurements (6-14 years). Using International Obesity Task Force criteria, BMI was classified as underweight, normal-weight, overweight and obesity. Sex- and age-specific prevalences were calculated.

RESULTS

From the 1930s, the prevalence of underweight was stable until a small increase occurred from 1950 to 1970s, and thereafter it declined into the early 2000s. Using 7-year-olds as an example, underweight changed from 10% to 7% in girls and from 9% to 6% in boys during the study period. The prevalence of overweight plateaued from 1950 to 1970s and then steeply increased from 1970s onwards and in 1990-2000s 15% girls and 11% boys at 7 years had overweight. The prevalence of obesity particularly increased from 1980s onwards and in 1990-2000s 5% girls and 4% boys at 7 years had obesity. These trends slightly differed by age.

CONCLUSION

Among Danish schoolchildren, the prevalence of underweight was greater than overweight until the 1980s and greater than obesity throughout the period. Thus, monitoring the prevalence of childhood underweight remains an important public health issue.

Estimating the causal effect of body mass index on hay fever, asthma and lung function using Mendelian randomization

BACKGROUND

Observational studies have shown that body mass index (BMI) is positively associated with asthma. However, observational data are prone to confounding and reverse causation. In Mendelian randomization, genetic variants are used as unconfounded markers of exposures to examine causal effects. We examined the causal effect of BMI on asthma, hay fever, allergic sensitization, serum total immunoglobulin E (IgE), forced expiratory volume in one-second (FEV1) and forced vital capacity (FVC).

METHODS

We included 490 497 participants in the observational and 162 124 participants in the genetic analyses. A genetic risk score (GRS) was created using 26 BMI-associated single nucleotide polymorphisms (SNPs). Results were pooled in meta-analyses and expressed as odds ratios (ORs) or β-estimates with 95% confidence interval (CI).

RESULTS

The GRS was significantly associated with asthma (OR=1.009; 95% CI: 1.004, 1.013), but not with hay fever (OR= 0.998; 95% CI: 0.994, 1.002) or allergic sensitization (OR=0.999; 95% CI: 0.986, 1.012) per BMI-increasing allele. The GRS was significantly associated with decrease in FEV1: β=-0.0012 (95% CI: -0.0019, -0.0006) and FVC: β=-0.0022 (95% CI: -0.0031, -0.0014) per BMI-increasing allele. Effect sizes estimated by instrumental variable analyses were OR=1.07 (95% CI: 1.03, 1.10) for asthma, a 9 ml decrease in FEV1 (95% CI: 2.0-15 mL decrease) and a 16 ml decrease in FVC (95% CI: 7.0-24 mL decrease) per 1 kg/m² higher BMI.

CONCLUSIONS

The results support the conclusion that increasing BMI is causally related to higher prevalence of asthma and decreased lung function, but not with hay fever or biomarkers of allergy.

Validation of a 5-year risk score of hip fracture in postmenopausal women. The Danish Nurse Cohort Study

SUMMARY

We evaluated the Women's Health Initiative (WHI) hip fracture risk score in 15,648 postmenopausal Danish nurses. The algorithm was well calibrated for Denmark. However, the sensitivity was poor at common decision making thresholds. Obtaining sensitivity better than 80% led to a low specificity of 61.4%.

INTRODUCTION

A new score based on data from the WHI has been designed to predict 5-year risk of hip fracture in postmenopausal women. The performance of the algorithm has not been validated in populations with different lifestyle characteristics and ethnicity. The aim of this study was to test the clinical performance of the algorithm in a large Danish cohort of postmenopausal Caucasian women against hip fracture.

METHODS

The Danish Nurse Cohort is a prospective risk factor and hormone therapy (HT) study established in 1993. Participants in the present analysis were 15,648 postmenopausal nurses. The calibration and diagnostic performance of the WHI algorithm was evaluated using fracture events captured in the Danish National Hospital Registry.

RESULTS

During 5 years of follow-up, 122 participants suffered a hip fracture (1.8/1,000 person years). The WHI algorithm predicted that 107 hip fractures would occur, indicating an underestimation of the number of fractures by 12%. To obtain sensitivity better than 80%, the cut-off value for 5-year risk was set to 0.5%, which was accompanied by a low positive predictive value of 1.9% and a low specificity of 61.4%. The algorithm predicted too many fractures in HT-users (12 observed, 22 expected) and too few in non HT-users (107 observed, 81 expected).

CONCLUSIONS

While the WHI algorithm was well calibrated on the Danish population, the clinical utility of the WHI algorithm in Danish postmenopausal women was limited by poor sensitivity at common decision-making thresholds and suboptimal in non-HT-users.