Table 1.
Characteristics of the included systematic reviews
| First author, year | Inclusion criteria | Outcomes | Assessment of dementia | Databases searched and search window | Articles included in review, articles included in meta-analysis | Number of patients | Design of the included articles | Main conclusion |
|---|---|---|---|---|---|---|---|---|
| Annweiler, 200911 | Data on serum 25(OH)D and cognitive status or diagnosed dementia, only studies with a healthy control group and use of a regression model for analysis in French and English | Cognitive status or diagnosed dementia | Not defined | MEDLINE, Cochrane library, PsychINFO between 1979 and December 2008 | 5 studies, N/A | 19 597 | Cross-sectional (n = 4), case–control (n = 1) |
Inconclusive results on the association between serum 25(OH)D and cognitive performance |
| Annweiler, 201314 | Any type of observational/ interventional studies, data on serum 25(OH)D and Alzheimer disease, adult humans, written in Latin alphabet | Alzheimer disease | Not defined | MEDLINE, PsychINFO from inception to May 2012 | 10 studies, 7 studies |
1005 | Case–control (n = 7), nested case–control (n = 2), prospective (n = 1) |
Patients with Alzheimer disease had lower serum 25(OH)D compared with matched controls |
| Annweiler, 201315 | Any type of observational/ interventional study, data on 25(OH)D and cognition, adult humans, written in Latin alphabet | Memory and executive dysfunction | N/A | MEDLINE, PsychINFO from inception to May 2012 | 17 studies, 12 studies |
39 975 | Cross-sectional (n = 11), prospective (n = 3), pre-post design (n = 2), RCT (n = 1) |
Lower serum 25(OH)D concentration predicts executive dysfunction (mental shifting, information updating, processing speed), uncertain association with episodic memory |
| Balion, 201212 | Any type of observational/interventional studies, data on 25(OH)D, cognition and dementia, humans aged >18 years, written in English | Cognitive function, dementia | NINCDS–ADRDA, DSM-III or IV, MMSE | MEDLINE, Embase, AMED, Cochrane library, PsychINFO from inception to August 2010 | 37 studies, 4 studies (Alzheimer disease), 10 studies (MMSE test) |
≅35 000 | Cross-sectional (n = 21, case–control (n = 10), prospective (n = 2), pre-post design (n = 1), RCT (n = 3) |
Lower 25(OH)D concentrations are associated with poorer cognitive function and a higher risk of Alzheimer disease |
| Cao, 201619 | Cohort studies including white patients, with follow-up for 1 year, data presented as risk or hazard ratios, with 95% CIs or with enough data to calculate these numbers, data on any type of dietary pattern or food consumption and dementia or mild cognitive impairment, on humans, and written in English | Dementia or mild cognitive impairment | Diagnostic codes | MEDLINE, Embase, BIOSIS, Cochrane library from 1997 to September 2014 | 3 studies, 3 studies |
12 702 | Prospective cohort (n = 3) | Low levels of vitamin D related to increase in dementia |
| Etgen, 201213 | Cross-sectional or longitudinal studies, at least 100 participants, data on vitamin D and cognitive impairment, results presented as odds or hazard ratios | Cognitive impairment | N/A | MEDLINE, Cochrane library, from 1980 to April 2012 | 15 studies, 7 studies |
7688 in meta-analysis | Cross-sectional (n = 9), prospective (n = 2) |
An increased risk of cognitive impairment in those with low vitamin D |
| Lopes da Silva, 20147 | Data on any type of plasma nutrient status and Alzheimer disease | Alzheimer disease | NINCDS–ADRDA, DSM III or IV | MEDLINE, Embase, Cochrane library, from 1990 to March 2012 | 5 studies, 5 studies |
865 | Case–control (n = 5) |
No association between low levels of vitamin D and Alzheimer disease |
| Shen, 201518 | Data on 25(OH)D concentration with cut-off point of <50 nmol/L and Alzheimer disease or dementia, results presented as odds, risk, or hazard ratios, written in English | Alzheimer disease and dementia | Not defined | MEDLINE, from inception to February 2015 | Alzheimer disease: 5 studies, 5 studies Dementia: 5 studies, 4 studies |
Alzheimer disease: 10 019 Dementia: 5073 |
Alzheimer disease: cross-sectional (n = 1), prospective (n = 4) Dementia: cross-sectional (n = 3), prospective (n = 2) |
Lower vitamin D status is associated with increased risk of developing Alzheimer disease and dementia |
| Sommer, 201720 | RCTs, prospective cohort and nested case–control, systematic reviews of longitudinal studies with data on the effect of sunlight exposure or vitamin D serum concentrations (as surrogate) and dementia, among adults, written in English and German | Dementia: Alzheimer disease vascular, frontotemporal, Lewy body |
Based on validated measurement scales | MEDLINE, Embase, Cochrane library, SCOPUS, Web of Science, ICONDA, PsychINFO, the Open Grey database, from 1990 to October 2015 | 6 studies, 5 studies |
18 933 | Prospective (n = 5), retrospective (n = 1) | Vitamin D deficiency increases the risk of dementia |
| van der Schaft, 201316 |
Observational studies with data on vitamin D (serum concentration or dietary intake) and cognition in adult humans, available measure of association | Cognition | Cognitive function test (e.g. MMSE, CDT) | Embase, PubMed from inception to June 2012 | 28 studies, N/A |
59 576 | Cross-sectional (n = 25), prospective (n = 6) |
Hypovitaminosis D is associated with worse outcome on one or more cognitive function tests and a higher frequency of dementia |
| Zhao, 201317 | Comparative analysis of 25(OH)D of individuals with Alzheimer disease against healthy population | Alzheimer disease | Not defined | MEDLINE, from 1983 to March 2012 | 6 studies, 6 studies |
892 | Case–control (n = 6) |
Patients with Alzheimer disease had non-significant lower levels of 25(OH)D relative to healthy controls |
25(OH)D, 25-hydroxyvitamin D; AMED, Allied and Complimentary Medicine Database; BIOSIS, BioSciences Information Service of Biological Abstracts; CDT, Wolf–Klein Clock Drawing Test; ICONDA, International Construction Database; MMSE, Mini-Mental State Examination; N/A, not applicable; NINCDS–ADRDA, National Institute Neurological and Communicative Disorders and Stroke–Alzheimer Disease and Related Disorders Association; RCT, randomised controlled trial; SCOPUS, Elsevier abstract and citation database.