Researchers from Northern Ireland and Ireland contacted participants aged 60 and over from a previous study into B vitamin intake, with 155 out of 255 potential subjects, all of whom showed normal cognitive function in the original study, able to participate in the new research.
In the original study participants over the age of 60 completed a cognitive function test – Folstein’s Mini Mental State Examination (MMSE) – in order to test their competence in recalling food intake. The new study compared these results to new MMSEs, along with blood tests and dietary surveys.
Participants had a mean age of 70 years, were predominantly female, well-educated and had a low rate of depression. The majority of participants were regular consumers of foods fortified with B vitamins (75%). "Dietary intakes compared favourably with current UK dietary recommendations as reflected in good overall B vitamin biomarker status."
“Our results showed that participants with lower status of vitamin B6 [PLP; the measure of active vitamin B6] at baseline were 3.5 times more likely to have a greater rate of cognitive decline over a [four year] follow-up period,” wrote the researchers in their paper, published in Nutrients.
The decline affected participants not only with deficient vitamin B6 levels, but also some with clinically sufficient levels of B6. The researchers suggested this showed that optimal vitamin B6 levels might be important for cognitive health in ageing.
In contrast to vitamin B6 (pyridoxine), the researchers did not find any links between other B vitamin status and cognitive decline in the subjects.
“Whilst elevated plasma homocysteine, low folate and, to a lesser extent, vitamin B12 [cobalamin] status have been frequently associated with cognitive decline there was no evidence of significant associations for these biomarkers in the current study,” wrote the researchers.
“The findings in the current study may be explained to some degree by the fact that vitamin B6 seemed to be the limiting nutrient within the cohort. There was a greater incidence of deficiency of vitamin B6 (11% clinical deficiency) compared with folate [vitamin B9, 3%] or vitamin B12 (0%),” they added.
They noted other studies support the idea that correcting sub-optimal levels of a B vitamin deficiency has a greater impact than providing additional B vitamins to people with optimal levels.
The researchers said they believed their study was the first longitudinal study to look at both dietary intake and biomarker status of B vitamins and their effect on cognitive health in ageing. But they highlighted a range of other studies which showed links between vitamin B6 deficiency and cognitive decline.