A pair of researchers from Shandong University of Technology in China has performed a meta-analysis showing that “lower vitamin D status may be associated with increased risk of developing Alzheimer’s disease [AD] and dementia.” Although the scientists caution that more research is needed to test the efficacy of vitamin D supplementation in reducing the risk of AD and dementia, their analytical results show a 21 percent greater risk for individuals with vitamin D levels lower than 50 nanomoles (nmol) per liter of blood volume.
The link between vitamin D and neurological health has been posited before, and some scientists consider it a strong enough connection to recommend deficiency screening and supplementation. This connection is biologically plausible, as vitamin D has been described as “a guardian of phenotypic stability […] with regard to reactive oxygen species (ROS) and Ca2+ [calcium] signaling systems.” Indeed, individuals with a particular vitamin D receptor gene polymorphism have a reduced risk of AD compared with individuals with different polymorphisms, providing more evidence for the importance of vitamin D in pathways that maintain neurological health.
A Mayo Clinic article on the topic of vitamin D and AD — an article that precedes the publication of the Chinese research — states that the recommended daily dose of vitamin D is 600 international units (IU) for adults younger than age 70 and 800 IU for adults 70 and older. The human body produces vitamin D during direct ultraviolet light (sun) exposure, and fatty fish (and their oils) are natural sources of vitamin D. Vitamin D-fortified foods are widely available, as well as standalone vitamin D supplements. According to US News, standing in the sun during the summer months in shorts and a tank top (full arm and leg exposure) for ten minutes allows a person of Caucasian descent to produce 10,000 IU of vitamin D. Individuals with darker skin would need longer sun exposure to produce the same amount.