open access
Vitamin D and Specific Causes of Death
While we mainly report on vitamin D and
all-cause mortality in this review, it is also important to briefly
summarize the
literature on specific causes of death, in order to
gain more knowledge on the potential pathways and mechanisms that may
link vitamin D and fatal events.
In observational studies, low 25(OH)D
levels have been associated with increased risk of mortality due to
cardiovascular diseases,
cancer, respiratory disease, and non-vascular,
non-cancer causes (
33,
35,
36,
43,
44,
49,
73-
76).
In the Mendelian randomization study by Afzal
et al.
it was reported that the odds ratio (95% CI) for cardiovascular
mortality for each decrease of 20 nmol/l in plasma 25(OH)D
was 1.13 (1.03 to 1.24), and the respective odds
ratio (95% CI) for the genetically determined 25(OH)D levels was 0.77
(0.55
to 1.08) (
68).
This may suggest that the association between low 25(OH)D and
cardiovascular deaths may not be causal. For cancer mortality,
the respective odds ratios (95% CI) for each
decrease of 20 nmol/l 25(OH)D was 1.10 (1.02 to 1.19) for plasma 25(OH)D
and
1.43 (1.02 to 1.99) for genetically determined
25(OH)D. These data
argue for causality with regard to the association
of vitamin
D deficiency and increased cancer mortality.
Meta-analyses of RCTs further support a
causal effect of vitamin D on cancer mortality. In the
Cochrane
meta-analysis by Bjelakovic
et al. involving 44,492 study participants from four trials, it was documented that
vitamin D3 supplementation statistically significantly reduced cancer mortality, with a risk ratio of 0.88 (95% CI=0.78-0.98). In line
with this, Keum
et al. also reported in their meta-analysis involving 44,260 participants that the RR for cancer mortality in the vitamin D-treated
versus the placebo-treated group was 0.88 (95% CI=0.78-0.98) (
77).
These findings along with various molecular anticancer effects of
vitamin D suggest that vitamin D supplementation
may
be useful for the prevention of cancer deaths. By
contrast, there was no effect in meta-analyses on cancer incidence,
suggesting
that vitamin D might rather be relevant for the
progression than for the initiation of cancer (77-79).
With regard to cardiovascular mortality, there was no significant effect of vitamin D as reported by Bjelakovic
et al. (
69). Although observational studies highlight vitamin D deficiency as a risk factor for cardiovascular events and strokes, most
RCTs did not show any effect of vitamin D on these outcomes (
69,
71,
80-
83).
It must, however, be acknowledged that
no published RCT on vitamin D
has been designed and statistically powered to assess
cardiovascular events. Existing knowledge on the
potential role of vitamin D for various other health outcomes have been
extensively
reviewed elsewhere (
1-
6,
84,
85).
....Regarding vitamin D research, there are some large ongoing RCTs on
vitamin D in the general population that will significantly
increase our knowledge on whether general vitamin D
supplementation in the older population has an effect on clinical
endpoints,
including mortality (92, 93).
It is, however, of concern that all large RCTs on vitamin D recruited
participants regardless of their 25(OH)D levels,
thereby increasing the probability of missing
beneficial effects of vitamin D supplementation in individuals with low
25(OH)D
concentrations. Null effects of such RCTs would
definitely argue against major effect sizes but definite answers on
whether
vitamin D supplementation has relevant effects on
mortality outcomes and other clinical endpoints should be derived from
RCTs
in severely vitamin D-deficient individuals, as
this is the target population for vitamin D interventions (92-95).
0 comments :
Post a Comment
Your comments?
Note: Only a member of this blog may post a comment.