A new epidemiological study arguments against vitamin D inducing later allergy (Parr et al., Vitamin A and D intake in pregnancy, infant supplementation, and asthma development: the Norwegian Mother and Child Cohort, Am J Clin Nutr 2018;107:789-798). Table 5 in the most recent paper shows no effect when correlating first year of life supplementation and later asthma.
But why did they authors not even cite our study from 2004 (Hyppönen et al. Infant Vitamin D Supplementation and Allergic Conditions in Adulthood Northern Finland Birth Cohort 1966. Ann. N.Y. Acad. Sci. 1037: 84-95) ??
Although our interest was more with allergy there have been clear effects on asthma that have been confirmed now two dozen times. Why did the authors miss that effect?
- The cohort consists of 115,000 children but only 55,000 are analyzed. So selection bias is omnipresent.
- A key issue is the definition of “asthma” as “having ≥2 pharmacy dispensations of asthma medication within a 12-month interval, which is more a “last resort” option than a correct diagnosis. “We cannot rule out some misclassication in our asthma outcome“. I agree.
- Another issue is the unrecorded vitamin supply by standard baby food in the range of 500-1000 IU/daily. Does it make any sense to test for excess supplements in a population that is already heavily exposed to >90%? “A limitation of this study is that we did not have data on nutrient intake from supplements in infant“. I agree, it makes the study worthless.
- The supplementation with cod liver oil, vitamin D and multivitamins is chaotic as been shown in the last row of table 5. In real life or just in this paper? Numbers are contradicting “Vitamin D only, sometimes” and “daily” do not add to the number given for “vitamin D only” in the “combined use” section.
- Supplementation at month 6 is even a late event if we believe that the first allergen contact under vitamin D exposure is being important.
So, still not need to drop the vitamin D hypothesis.