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Randomized controlled trial finds that high dose vitamin D supplementation (4,000 IU/day) for 18 weeks improves visual memory in healthy adults but low-dose vitamin D (400 IU/day) does not.
Serum 25 hydroxy vitamin D levels increased significantly more in the high dose group (from 27 ng/ml to 52 ng/ml) than the low dose group (24 ng/ml to 34 ng/ml). What is interesting is that even though 34 ng/ml is considered sufficient, it still was not enough to improve visual memory.
It has been suggested that visual memory tasks place greater demands on cognitive processing, organization, planning, and overall executive functioning than do verbal memory tasks, and require more fluid cognitive processes.
Dear Dr. Rhonda, have you seen a recent New York Times article stating that vitamin D supplementation is unnecessary, and that the studies that supported this were paid by the vitamin supplementation industry. I would really like to hear your take on this, please! Here is the link to the article, in case you haven’t seen it: https://www.nytimes.com/2017/04/10/health/vitamin-d-deficiency-supplements.html
The full transcript of this article is available online. The research was paid for by an internal University seed grant. Seed funding is made available to new researchers to help them get their career started and comes without bias or strings attached. The article can be read here: https://www.researchgate.net/publication/313358592_Does_high_dose_vitamin_D_supplementation_enhance_cognition_A_randomized_trial_in_healthy_adults
The NYTimes article that you refer to does not appear to address this research specifically.