[Relationship between 25-hydroxy vitamin D and cognitive status in older adults: the COGNIDAGE study]

The aim of the COGNIDAGE study was to examine the association between 25(OH)D and cognitive status in a group of elderly patients with vitamin D deficiency and high burden of comorbidities attending Geriatric Outpatient Clinics.

We studied the relationship between 25(OH)D and cognitive functions taking into account comorbidities and cognitive functions assessed by MMSE (Mini Mental State Examination), CDT (Clock Drawing Test) and CIRS (Cumulative Illness Rating Scale), in 132 consecutive elderly patients with low levels of 25(OH)D (<10 ng/ml) compatible with the condition of vitamin deficiency. The association among 25(OH)D levels, MMSE score, CDT score and CIRS scores were analyzed using Pearson correlation. All the elderly patients received an adequate vitamin D supplementation and were reassessed after 6 months.

At baseline, mean MMSE and CIRS scores were: 21.8+5.56 and 2.96 +1.63 respectively. Mean CDT score was 3,66+-2.05. No associations were found between 25(OH)D levels and global cognitive function. A significant relationship was observed between the total CIRS score and 25(OH)D levels (r=0.305; p=0.000) as well as between total CIRS score and MMSE (r=-0.375; p=0.000). After 6 months, 83.9 % had 25(OH)D levels >20 ng/ml. Mean MMSE and CDT scores were 22.20+-5.76 and 3.90+-2.06 respectively. There was no significant correlation among 25(OH)D, MMSE and CDT scores while a significant correlation was found between 25(OH)D and CIRS- severity score (r=0.275; p=0.001) and between MMSE and total CIRS scores (r=-0.247; p=0.005 for CIRS-comorbidities; r=-0.184; p=0.04 for CIRS-severity). A post hoc evaluation on two subgroups of elderly patients (the first with vitamin D deficiency without cognitive impairment, the second with vitamin D deficiency and dementia) showed a statistically significant difference (p=0.00001) regarding the CIRS-comorbidities scores.

In our cohort of elderly patients with a high burden of comorbidities, 25(OH)D low levels (<10 ng/ml) are not associated with MMSE and CDT scores. There is no statistically difference among the levels of 25(OH)D and MMSE and CDT scores after 6 months. The strong correlation we found regarding CIRS-comorbidities in the two sub-groups suggests that vitamin D deficiency may play a role in promoting cognitive impairment only with comorbidities.