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Featured articles 2015

Prenatal exposure to persistent organic pollutants and offspring allergic sensitization and lung function at 20 years of age.

Prenatal exposures to persistent organic pollutants (POPs) have been associated with asthma medication use and self-reported symptoms, but associations with lung function and allergic sensitization have been minimally explored. The aim of the study was to examine the associations between prenatal exposures to POPs and allergic sensitization and lung function in 20-year-old offspring.

We used a Danish cohort of 965 pregnant women established in 1988-1989 to examine the aim. Six polychlorinated biphenyl (PCB) congeners, hexachlorobenzene (HCB), and dichlorodiphenyldichloroethylene (p,p'-DDE) were quantified in archived maternal serum drawn in gestational week 30 (n = 872). Offspring of the originally enrolled mothers were invited to participate in a clinical examination at age 19-20 years. Among those with available maternal exposure information, 421 offspring attended attended the clinical examination including measurements of allergic sensitization (serum-specific IgE ≥ 0.35 kUA /L) (n = 418) and lung function [forced expiratory volume in one second (FEV1 ) and forced vital capacity (FVC)] (n = 414).

We found no associations between maternal concentrations of POPs and offspring allergic sensitization at 20 years of age. Maternal concentrations of POPs were, however, positively associated with offspring airway obstruction (FEV1 /FVC < 75%). Compared to offspring in the first tertile of exposure, offspring in the third tertile of dioxin-like PCB exposure had an OR of 2.96 (95% CI: 1.14-7.70). Similar associations for non-dioxin-like PCBs, HCB, and p,p'-DDE were 2.68 (1.06-6.81), 2.63 (1.07, 6.46), and 2.87 (1.09, 7.57), respectively. No associations were observed with reduced lung function (FEV1 % of predicted value < 90%).

Our data indicate that prenatal exposure to POPs appears to be associated with airway obstruction but not allergic sensitization at 20 years of age. The findings support that chronic obstructive lung diseases may have at least part of their origins in early life.

Hansen S, Strøm M, Olsen SF, Dahl R, Hoffmann HJ, Granström C, Rytter D, Bech BH, Linneberg A, Maslova E, Kiviranta H, Rantakokko P, Halldorsson TI. Prenatal exposure to persistent organic pollutants and offspring allergic sensitization and lung function at 20 years of age. Clin Exp Allergy. 2016 Feb;46(2):329-36. doi: 10.1111/cea.12631. PubMed PMID: 26333063. 

Key words: Persistent organic pollutants, allergic sensitization, lung function, fetal programming

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Infant Growth and Risk of Childhood-Onset Type 1 Diabetes in Children From 2 Large Scandinavian Birth Cohorts

Type 1 diabetes mellitus is one of the most common chronic diseases with onset in childhood, but environmental risk factors have not been convincingly established. We tested whether increased growth during the first year of life is associated with higher risk of childhood-onset type 1 diabetes in the Norwegian Mother and Child Cohort Study (MoBa) and the Danish National Birth Cohort (DNBC). Children born between February 1998 and July 2009 were included, totalling 99 832 children. MoBa contributed with 59 221 children (51.2% boys and 48.8% girls; mean age at end of follow-up, 8.6 years [range, 4.6-14.2 years]) and DNBC 40 611 children (50.6% boys and 49.4% girls; mean age at end of follow-up, 13.0 years [range, 10.4-15.7 years]).

The incidence rate of type 1 diabetes from age 12 months to the end of follow-up was 25 cases per 100 000 person-years in DNBC and 31 cases per 100 000 person-years in MoBa. The change in weight from birth to 12 months was positively associated with type 1 diabetes (pooled unadjusted HR = 1.24 per 1-SD increase; 95% CI, 1.11-1.39; pooled adjusted HR = 1.24 per 1-SD increase; 95% CI, 1.09-1.41). There was no significant association between length increase from birth to 12 months and type 1 diabetes (pooled unadjusted HR = 1.06 per 1-SD increase; 95% CI, 0.93-1.22; pooled adjusted HR = 1.06 per 1-SD increase; 95% CI, 0.86-1.32). The associations were similar in both sexes.

This study was the first prospective population-based study, to our knowledge, providing evidence that weight increase during the first year of life is positively associated with type 1 diabetes. The study supports the early environmental origins of type 1 diabetes.

Magnus MC, Olsen SF, Granström C, Joner G, Skrivarhaug T, Svensson J, Johannesen J, Njølstad P, Magnus P, Størdal K, Stene LC. JAMA Pediatr. 2015 Dec 7;169(12):e153759. doi: 10.1001/jamapediatrics.2015.3759. Epub 2015 Dec 7.

Key words: epidemiology; early growth; childhood diabetes, DNBC; MoBA, Nordic Birth Cohorts

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Maternal intake of fat in pregnancy and offspring metabolic health
- a prospective study with 20 years of follow-up.

Study of adult populations have suggested that the amount and type of fat we consume may influence our risk of diabetes and heart disease. However, it is currently unclear whether the fat women eat during pregnancy can affect the way their children develop in utero and their future risk for these chronic diseases. In this study, we specifically examined the children’s body mass index (BMI) and waist circumference measured at age 20. BMI and waist circumferences were used as indicators of the amount of fatty tissue in the children, an important risk factor for the abovementioned chronic diseases. Maternal intake of three types of fat during pregnancy: saturated (found primarily in butter, dairy, and meat), monounsaturated (in olive oil and avocados, but also in processed foods as trans fats), and polyunsaturated (in vegetables oils, nuts, fish), were related to the children’s BMI and waist circumference 20 years later.

We found that the type of fat consumed by mothers in pregnancy was not related to BMI or waist circumference in their daughters. Among the sons, higher maternal monounsaturated fat intake in pregnancy lead to a small increase in their waist circumference. Additionally, if the mothers’ total fat intake was more than 35% of their daily calories, their sons were more likely to have a higher BMI and waist circumference. We concluded that eating a high-fat diet in pregnancy may influence BMI and waist circumference in male children. We speculate that the association found with monounsaturated fat most like relate to intake of trans fats from processed foods rather than foods like olive oil and avocados, but this would have to clarified in studies with better information on trans fats.

Maslova E, Rytter D, Bech BH, Henriksen TB, Olsen SF, Halldorsson TI. Maternal intake of fat in pregnancy and offspring metabolic health - A prospective study with 20 years of follow-up. Clin Nutr. 2015 Apr 9. [Epub ahead of print] PubMed PMID: 25933442

Key words: fetal programming, fat intake, pregnancy diet, metabolic health 

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Dietary protein-to-carbohydrate ratio and added sugar as determinants of excessive gestational weight gain: a prospective cohort study

From prior studies we know that excessive gestational weight gain (GWG) in pregnancy is associated with complications for both the mother and the child, including gestational diabetes, hypertension, and high birth weight. Understanding the factors that determine GWG would allow for interventions early on to improve pregnancy outcomes. Dietary intake has been found to influence GWG in other studies, but evidence is conflicting and still quite limited. In non-pregnant adult populations a high-protein diet has been shown to weight loss and improved weight maintenance. We therefore hypothesized that a similar relation may exist for GWG in pregnant women.

In this study we had data on dietary intake of more than 45,000 Danish women who were pregnant between 1996 and 2002. We examined the relation between their intake of protein and carbohydrates and the rate of GWG (in grams per week). We found that women who consumed a high protein-to-carbohydrate (PC) ratio gained less GWG compared to women with a lower PC ratio in their diet. The results were stronger in women who started their pregnancy already overweight compared to normal-weight women.

Since a high PC ratio may result from either a high protein intake or low carbohydrate intake, we decided to focus on a component of carbohydrates that may increase GWG: added sugar. We found that pregnant women with higher intake of sugar gained more weight in pregnancy compared to those who ate less added sugar. This averaged out to about 1.4 kg (or 7%) higher weight gain across the entire pregnancy.

Key words: epidemiology; nutrition and dietetics; obstetrics

Maslova E, Halldorsson TI, Astrup A, Olsen SF. BMJ Open. 2015 Feb 10;5(2):e005839. doi: 10.1136/bmjopen-2014-005839

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The long-term programming effect of maternal 25-hydroxyvitamin D in pregnancy on allergic airway disease and lung function in offspring after 20 to 25 years of follow-up

Vitamin D in high doses may increase risk of asthma

Allergic disease is one of the most common chronic conditions worldwide. Symptoms usually develop early in childhood, which suggests that early life exposures may influence the risk of developing allergic disease. Low levels of vitamin D during pregnancy has been identified as a potential risk factor for developing allergic disease in the child but findings from previous studies have been conflicting. Furthermore, it is not known whether low levels of vitamin D in pregnancy has the potential to influence the risk of allergy development past childhood. Now, in a study recently published in The Journal of Allergy and Clinical Immunology, S. Hansen and colleagues present the first results from a long-term follow-up of Danish adults whose mothers participated in a study when they were pregnant.

In 1988-1989, 965 pregnant women were enrolled in the study and gave a blood sample, which was used to measure levels of vitamin D. The children were tracked from their birth until the end of 2013, when they were around ~25 years of age, in Danish population-based disease registries by using the unique personal identification number given to all Danish citizens. We obtained information about the children’s use of asthma medication and allergic rhinitis medication, and their hospitalizations due to asthma during the follow-up period. Furthermore, around 50% of the children participated in a clinical examination in 2008, when they were ~20 years old, where they had a blood sample drawn and their lung function was measured.

The authors found no evidence that high vitamin D levels (>125 nmol/L) in pregnancy protected against allergic disease in the child. In contrast, those children whose mothers had high levels of vitamin D had an increased risk of having been hospitalized for asthma compared to children of mothers who had recommended levels of vitamin D (75-125 nmol/L). There was furthermore a lower risk of using asthma medication and of asthma hospitalizations among children whose mothers had low vitamin D levels in pregnancy (<50 nmol). The authors did not see any association between vitamin D levels in pregnancy on lung function or allergic rhinitis.

Therefore, this study does not support high dose vitamin D supplementation to pregnant women with the purpose of preventing allergic disease in their children. Results from intervention studies are on their way and will hopefully provide further information on the role of vitamin D in pregnancy and allergic disease.

Tag line: The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

Key words: cohort, pregnancy, fetal programming, 25-hydroxyvitamin D, asthma, allergic rhinitis, lung function.

Susanne Hansen, Ekaterina Maslova, Marin Strøm, Allan Linneberg, Thorhallur I. Halldorsson, Charlotta Granström, Ronald Dahl, Hans Jürgen Hoffmann, Sjurdur F. Olsen. Journal of Allergy and Clinical Immunology, Available online 30 January 2015

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Last revised 21 August 2017