Dr. Jacqueline Petterson, a neuroscientist at the University of British Columbia, recently discovered that verbal fluency peaks when an individual’s vitamin D level is between 40 and 50 ng/ml (100 – 125 nmol/l.)
A similar study in hemodialysis subjects found many more cognitive domains, with the exception of memory, were impaired by low vitamin D levels.
Shaffi K, Tighiouart H, Scott T, Lou K, Drew D, Weiner D, Sarnak M. Low 25-hydroxyvitamin D levels and cognitive impairment in hemodialysis patients. Clin J Am Soc Nephrol. 2013 Jun;8(6):979-86. doi: 10.2215/CJN.10651012. Epub 2013 Feb 28.
This was also true of elders receiving nursing home services, again with no memory benefit.
Buell JS, Scott TM, Dawson-Hughes B, Dallal GE, Rosenberg IH, Folstein MF, Tucker KL. Vitamin D is associated with cognitive function in elders receiving home health services. J Gerontol A Biol Sci Med Sci. 2009 Aug;64(8):888-95. doi: 10.1093/gerona/glp032. Epub 2009 Apr 17.
Another study which looked at cognitive performance in middle age and youthful elders had the same findings of the two studies above.
Lee DM, Tajar A, Ulubaev A, Pendleton N, O’Neill TW, O’Connor DB, Bartfai G, Boonen S, Bouillon R, Casanueva FF, Finn JD, Forti G, Giwercman A, Han TS, Huhtaniemi IT, Kula K, Lean ME, Punab M, Silman AJ, Vanderschueren D, Wu FC; EMAS study group. Association between 25-hydroxyvitamin D levels and cognitive performance in middle-aged and older European men. J Neurol Neurosurg Psychiatry. 2009 Jul;80(7):722-9.
The graph below shows Petterson’s findings:
Figure 1. Spline regression plot showing the relationship between verbal fluency scores and 25-hydroxyvitamin D [25(OH)D] levels, adjusted for age, education, sex, mood (Beck Depression Inventory–II, BDI–II), body mass index (BMI) and physical activity.
“In conclusion, vitamin D levels exceeding 100 nmol/L (40 ng/ml) were found to be associated with significantly better performance on a verbal (phonemic) fluency task, which primarily assesses executive functioning. This implies that the optimal level for cognition is higher than that for bone health, and higher than previous studies have suggested. Spline analyses suggest that the relationship is not entirely linear, with an optimal level possibly around 120 nmol nmol/L (50 mg/ml).”