However, this positive association only applied to those with a low educational level, which could be explained by the phenomenon of cognitive reserve.
Cognitive reserve is the idea used to explain why the same degree of brain damage or neuropathology may affect some people and not others.
“Higher education has been proposed as a potential modulator of cognitive reserve, improving the ability to cope with neurological damage,” the researchers wrote in the British Journal of Nutrition.
The study looked at the cognitive health of 1009 individuals 13-years after their 25-Hydroxyvitamin D (25(OH)D) plasma levels were recorded as part of the French ‘Supplémentation en Vitamines et Minéraux Antioxydants’ study (SU.VI.MAX, 1994–2002).
This latest paper used this baseline data as well that from the SU.VI.MAX 2 observational follow-up study gathered in 2007–9.
Testing cognitive performance
Cognitive performance was assessed by trained neuropsychologists using a variety of tests.
Lexical-semantic memory was tested by a phonemic and semantic fluency task, episodic memory by a RI-48 cued recall test, short-term memory by forward digit span, working memory by backward digit span and finally mental flexibility by a number–letter switching task (of the Delis–Kaplan Trail Making Test).
The researchers noted that the lack of cognitive assessment at baseline prevented them from tracking cognitive decline. This meant that it was possible that those with low vitamin D status already had worse cognitive performance at baseline.
Making the links
Vitamin D status was most strongly associated with the performance of working memory among individuals with low education. This result echoed previous findings of meta-analysis.
Among participants with secondary education only, there was no association between vitamin D and any cognitive variable except phonemic fluency, where better outcomes were found in individuals with higher vitamin D levels.
The researchers ran additional models adjusting for incident of cardiovascular disease and history of diabetes and hypertension. However, this showed similar results.
Source: British Journal of Nutrition
Published online ahead of print, doi:10.1017/S0007114515001051
“Midlife plasma vitamin D concentrations and performance in different cognitive domains assessed 13 years later”
Authors: K. E. Assmann, M. Touvier, V. A. Andreeva, M. Deschasaux, T. Constans, S. Hercberg, P. Galan and E. Kesse-Guyot