A recently published RCT examined the impact of high-dose vitamin D3 supplementation (2400 IU daily in addition to the recommended 400IU) versus standard 400 IU dose on the cognitive performance of 10-year-olds.

The intervention took place when their mothers were 24 weeks gestation to 1 week postpartum. Cognition was measured in 498 children (247 from the high dose group and 251 from the standard dose group). Tests included reaction time, sustained attention, motor function, verbal memory, speed of processing, planning and more.

Out of the 11 tests, there were no significant differences between the groups in 8 cognitive functions. However, high-dose supplementation was positively associated with verbal memory, visual memory and flexibility or set shift.

There were limitations of the study, including a lack of data on parental intelligence and psychopathological conditions, although education and income were considered. In addition, these tests were only conducted at one point during childhood, and supplementation was given in the second half of pregnancy, not from the beginning.

In the UK, vitamin D is recommended at a dose of 400 IU (10mcg) per day from the start of pregnancy. Further research is needed on the long-term impact of vitamin D supplementation on cognition and overall health.