Published in the Journal of Nutritional Science the study looked at the impact of twice-weekly servings of various kinds of fish for 784 children aged 8- to 11- years as part of a school lunch. The children received three months of school lunches and three months of control ‘habitual’ lunches packed lunch brought from home.
They found this relatively small dietary change increased vitamin D serum levels in winter months November to February compared to the control.
The school meals increased fish intake by 48% compared to the nine grams per day of the control, meaning an increased vitamin D intake of 0.9 micrograms (µg) per day.
“The daily vitamin D intake of the children included in this secondary outcome study increased by 31–64% during the ad libitum school meal period compared with the control period. This is a substantial effect considering the low intake continuously reported in European children and considering the scarce amount of food sources that are naturally rich in vitamin D.”
Danish daily recommendations state ten micrograms of vitamin D for children.
However, the same could not be said for serum levels in the summer months of March to June, despite the same intakes. Commenting on the difference the researchers speculated that this could be due to a change in the time set aside for eating – extended from the usual 15 minutes to up to 25 minutes for the school meal periods.
They said the extra time for eating the school meals inside may have meant less time spent playing outside. While this would have little impact in the darker winter months, in the summer this could have ironically impacted the amount of vitamin D the children got from sunlight.
This was a key practical point that should be considered in future studies and policies, the researchers said.
The study was conducted by researchers from the University of Copenhagen, the National Food Institute at the Technical University of Denmark and the Aalborg University Hospital as part of the OPUS (Optimal well-being, development and health for Danish children through a healthy New Nordic Diet) School Meal Study.
Growth hormone upped?
The researchers also looked at markers related to bone health including levels of parathyroid hormone, osteocalcin, insulin-like growth factor-1 (IGF-1), bone mineral content, bone area and bone mineral density.
No consistent results were seen for these markets. However they did record an “unexpected” slight increase in parathyroid hormone levels for the experiment lunch compared to the control.
“It is interesting to consider that parathyroid hormone (PTH) has been recognised to increase as a reflection of adolescent growth, and, although highly hypothetical, a potential rationale for the unexpected effect on PTH might be a speculated growth-related stimulation triggered by the school meals,” they wrote.
They said this point in particular warranted further investigation.
Source: Journal of Nutritional Science
Vol. 4, e.26, pp 1-10, doi:10.1017/jns.2015.15
“Effects of school meals with weekly fish servings on vitamin D status in Danish children: secondary outcomes from the OPUS (Optimal well-being, development and health for Danish children through a healthy New Nordic Diet) School Meal Study”
Authors: R. A. Petersen, C. T. Damsgaard, S.M. Dalskov, L. B. Sørensen, M. Fiil Hjorth, R. Andersen, I. Tetens, H. Krarup, C. Ritz, A. Astrup, K. F. Michaelsen and C. Mølgaard