Vitamin D and Health

Summary - Infectious diseases
6.311 The majority of evidence in this area relates to use of vitamin D as a therapeutic agent in patients with preexisting
disease and whether vitamin D can reduce severity or progression of the disease. Findings from such
studies are not applicable to the general population.
6.312 Evidence on vitamin D and infection is inconsistent and mainly observational. RCTs do not generally show a
beneficial effect of vitamin D supplementation on infectious disease risk.
6.313 No RCTs on the effect of vitamin D supplementation for prevention of TB could be identified. Observational
studies report a positive association between serum 25(OH)D concentration and TB risk. Studies examining
associations between VDR gene polymorphisms and susceptibility to TB are inconclusive.
6.314 Out of 3 systematic reviews/meta-analyses of RCTs on the effect of vitamin D supplementation on RTIs, 1
reported beneficial effects of vitamin D supplementation in reducing RTI risk, 1 reported no effect and 1
reported conflicting results. The majority of RCTs published since the meta-analyses also did not find that
vitamin D supplementation reduced RTI risk. Findings from cohort studies are generally supportive of an inverse
association between serum 25(OH)D concentration and RTIs, with serum 25(OH)D concentrations ranging
between < 25 and < 50 nmol/L associated with increased risk for developing RTIs.
Neuropsychological functioning (cognitive function, depression, dementia, autism, schizophrenia)
6.315 The effect of vitamin D on brain function is an area of growing interest but, for many conditions, the
evidence base is currently limited. From a biological perspective, vitamin D receptors and 1-
α hydroxylase have been identified in the cerebral cortex and cerebellum suggesting that the brain
may synthesise 1,25(OH) 2 D to regulate local functions. Animals deprived of vitamin D early in
development show evidence of abnormal brain development. This raises the possibility that vitamin D
might impact on various aspects of brain function (such as mood or cognition) or diseases caused by
abnormal brain function (such as autism and schizophrenia).
6.316 IOM Report: The IOM considered the effect of vitamin D on cognition & dementia, autism,
depression, schizophrenia. The report noted that the evidence base comprised observational data
mostly from cross-sectional studies with shortcomings in study design and quality.
Evidence considered (Tables 53-54, Annex 2)
Cognition and dementia
Intervention studies
6.317 Two small studies examined the effects of vitamin D supplements on cognition in adults over a few
weeks (Przybelski et al., 2008; Stein et al., 2011). Both had significant design weaknesses. In an
unblinded study (Przybelski et al., 2008) of nursing home residents (n=63; mean age, 87y), participants
were supplemented with vitamin D 2 (1250 µg/50,000 IU) 3 times/week for 4 weeks if their serum
25(OH)D concentration was < 62 nmol/L; participants in the comparison group (with 25(OH)D
concentration > 62 nmol/L) were not given a placebo. Vitamin D 2 supplementation had no effect on
cognition.
6.318 Stein et al. (2011) examined the effect of high dose vitamin D on memory and disability on community
dwelling individuals with mild/moderate Alzheimer’s disease (n=63; median age, 77.5y). All
participants were supplemented daily with vitamin D 2 (25 µg/1000 IU) throughout the trial. After 8
weeks run-in, participants were randomised to receive placebo or a high dose vitamin D 2 supplement
91