Swallow migration to Africa, for vitamin D?

This video is about barn swallows in Africa.

Translated from Vroege Vogels in the Netherlands:

Barn swallows and vitamin D

Psychiatrist William Bohlmeijer has a theory: according to him, birds like barn swallows migrate to Africa for several reasons, including getting their required amount of vitamin D. In psychiatry, it is known that there is a link between depression and vitamin D deficiency. Sunlight is important for humans; the barn swallow gets its vitamin D from its diet of insects. At present, the hypothesis is being tested scientifically.

Willem Bohlmeijer is making a documentary about his theory. On the basis of the migration of the barn swallows from the Achterhoek to their winter destination in Zambia, in the film knowledge and the latest scientific findings about the importance of vitamin D for the human body are discussed.

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