By Louise Pedersen, MD, PhD
Chairman: Anders Juul
Opponent: Freddy Karup Pedersen
Opponent: Birgitta Strandvik
Polyunsaturated fatty acids (PUFA) and vitamin D are important for fat and bone metabolism but the intake is declining in Western societies with a potential deleterious effect on growth and bone health.
Dietary PUFA composition favors the intake of omega-6 (n-6 PUFA) compared to omega-3 (n-3 PUFA). Hormones (eicosanoids) from n-6 PUFA induce fat cell differentiation and an intake high in n-3 PUFA relative to n-6 PUFA is hypothesized to inhibit differentiation and hypertrophy of adipose cells and subsequently the risk for obesity. Identification of dietary components with effects on fat tissue growth early in life is essential for preventive steps against development of overweight and obesity.
Vitamin D promotes bone mineralization and growth through regulation of the calcium homeostasis, and via activation of vitamin D receptors on bone and cartilage forming cells. However vitamin D insufficiency is increasing in many Western societies.
Bone mineral accrual in childhood influences later bone health and optimization may be preventive against the development of demineralizing skeletal disorders.
The purpose of this PhD thesis is to investigate the association between n-3 PUFA in breastmilk and BMI development, and fat percentage; serum vitamin D status in cord blood and height development and bone mineralization; and serum vitamin D status at 4 years and bone mineralization.
This is performed in the Copenhagen Prospective Study of Asthma in Childhood (COPSAC2000).
In Study 1, breast-milk n-3 PUFA exposure from 281 mothers was expressed as docosahexaenoic acid (DHA) and n-6/n-3 PUFA-ratio. In 222 of the children, we registered BMI from 2-7 years and age and BMI at adiposity rebound, parameters predictive of adiposity risk. In 207of the children, we furthermore measured body fat percentage by dual energy Xray absorptiometry (DXA) at 7 years.
We found a significant inverse association between DHA and BMI from 2-7 years, body fat 8 percentage at 7 years and a positive association with age at adiposity rebound, but the latter was only significant in the girls.
We found no association between the ratio of n-6/n-3 PUFA in breast-milk and any of the growth parameters.
From these results, we conclude that early dietary DHA content may have an impact on fat tissue formation, and a potential preventive effect on the development of obesity.
In Study 2 and 3, we have examined the relationship between:
1: 25-hydroxy vitamin D (25OHD) in cord blood, and
– Height Development from 2 weeks to 7 years in 222 children
– Bone mineralization by ultrasound of proximal phalanges at 3 years in 159 children.
– Bone width and mineralization at 7 years by DXA in 189 children.
2: 25-hydroxy vitamin D (25OHD) in children at 4 years and
– Bone mineralization by ultrasound of proximal phalanges at 3 years in 228 children.
– Bone width and mineralization at 7 years by DXA in 249 children.
Regions of interest were appendicular skeleton (arms + legs), spine, total body less head and the skull.
Mineralization was defined as the mineral content (g hydroxyapatite) adjusted for projected bone area, height, weight and age and bone width was defined as projected bone area adjusted for height, weight and age.
For 25OHD in cord blood we found a significant association to length/height development from 2 weeks to 7 years but not to bone mineralization or width at 3 or 7 years.
For 25OHD at 4 years, we found a significant association to skull mineralization at 7 years, but not to mineralization in any other regions, a non-significant association to mineralization at 3 years and no association to bone width.
From these results, we concluded that intrauterine and childhood vitamin D status has a promoting effect on bone growth and mineralization.