Page 136 - Vitamin D and Cancer

6 Vitamin D: Cardiovascular Function and Disease 123

cases compared with controls, which was attributed by the authors to a vitamin D
lowering effect from thiazide diuretics [90]. A cross-sectional study from New
Zealand found a weak inverse association between plasma 25OHD and diastolic
blood pressure which was not significant after adjusting for age and season [42].
Small case–control studies (with <30 cases) reported either increased [91] or
similar [92] serum 25OHD levels in cases compared with controls. A further nested
case–control study from New Zealand with a much larger sample (186 cases),
reported similar 25OHD levels in cases and controls matched by age, sex, ethnicity,
and season [93].
Inconsistent findings have also been reported in studies of blood levels of the
active metabolite 1,25(OH) D and blood pressure. A cross-sectional study of 373
2
women from Iowa reported a significant positive association between serum
1,25(OH) D and blood pressure after adjusting for age, BMI, and current thiazide
2
use [94]. This finding was confirmed in small case–control studies which reported
significantly higher levels of both 1,25(OH) D and PTH in cases [91, 92]. However,
2
other studies have reported inverse associations between 1,25-dihydroxyvitamin D
and blood pressure [95–97].
A small number of experimental studies were also carried out during this period.
The first two in Sweden showed that active vitamin D (alphacalcidol) lowered
blood pressure in patients with intermittent hypercalcemia or impaired glucose
tolerance [98, 99]. Although both of these studies were double-blind with controls,
in one of them there is a reported high dropout rate, from 86 participants at baseline
to 25 remaining at follow-up after 6 months treatment, raising the possibility of a
withdrawal bias [98]; while in the other, the reduction in blood pressure was limited
to those with hypertension (blood pressure ³ 150/90) [99]. A further study by the
same research group reported a reduction in blood pressure in 14 men with impaired
glucose tolerance given alphacalcidol over 18 months, but the lack of control group
negates the findings from this study [100]. In contrast, two studies of participants
sampled from the community did not show an effect of vitamin D on blood pres-
3
sure. One was a US study from Oregon (n = 65) which found that 1,000 IU vitamin
D /day (with calcium) for 3 years did not show any effect on blood pressure [101],
3
despite this dose increasing 25OHD levels by about 30 nmol/L [102]. The other
study was carried out in the UK (n = 189) and found that a single 100,000 IU dose
of vitamin D had no effect on blood pressure after 6 weeks, when compared with
3
controls, although the difference in 25OHD at 6 weeks between the groups was
only 8.6 ug/mL (21.5 nmol/L) [44].

6.3.3.2 Cardiac Function

At this time, isolated case reports started to appear of congestive heart failure with
vitamin D deficiency and hypocalcemia, in both adults and children, being success-
fully treated by vitamin D (in combination with calcium) [103–105]; while chil-
dren with severe rickets without clinical signs of heart failure were found
pretreatment to have thickened interventricular septa which returned to normal