A new randomized controlled trial out of Spain has found that low dose vitamin D supplementation does not change lipid levels but does lower blood pressure in young healthy women.
Past research has shown that increased vitamin D levels is associated with better overall cardiovascular health. However, if there is a causal relationship, it is still unclear whether vitamin D benefits the heart through regulation of blood pressure, reducing lipids levels, preserving insulin secretion, some other way or by a combination of these.
Additionally, almost all studies examining vitamin D and cardiovascular health have looked at cardiovascular disease patients, not healthy populations. In the current study, researchers wanted to know what effect vitamin D supplementation might have in a healthy population.
They enrolled 165 young healthy women into their trial and divided them into three groups. Those that had low levels of iron were randomly assigned to receive vitamin D-fortified skim milk or to receive a placebo skim milk. Those that had healthy iron levels were assigned to a reference group. In total, 54 women were assigned to the vitamin D group, 55 to the placebo group, and 56 to the reference group.
The women in the vitamin D or placebo group were required to drink one 500 mL carton of skim milk per day. These cartons of milk contained 15 mg of iron per unit. The vitamin D group’s milk cartons contained 200 IU of vitamin D per carton in addition to the iron.
The women underwent this daily fortified milk consumption for 16 weeks. At the end of the trial, the researchers found:
- The vitamin D group’s vitamin D levels increased from 24.9 ng/ml at baseline to 28.5 ng/ml, and the placebo group’s vitamin D levels stayed level, from 25.16 ng/ml at baseline to 25.28 ng/ml after 16 weeks.
- Glucose and lipid levels did not change over time in either the vitamin D or the placebo group, and the researchers observed no difference between groups.
- Over time, LDL cholesterol increased in the placebo group but slightly decreased in the vitamin D group. However, this was not quite statistically significant (p=0.07).
- In the vitamin D group, systolic and diastolic blood pressure decreased significantly compared to the placebo group, which saw no change in blood pressure (p=0.017).
The researchers concluded,
“Consequently, the results of this randomized placebo-controlled trial show that consumption of a daily physiological dose of cholecalciferol (i.e., the Spanish RDA) in a fortified food was able to significantly decrease blood pressure, and support a direct effect of vitamin D metabolites on the renin-angiotensin-aldosterone system and blood pressure.”
The researchers pointed out that, although the use of healthy women was novel, it could be considered a limitation to the study. Other limitations include the use of only one level of fortification and that the effects of fortified food was not compared to other supplements.
A further limitation is the very small dose the researchers used. In their conclusion, they note that the dose of 200 IU is physiological, but it is not physiological by definition. A physiologic dose describes a dose that mimics the potency of what would occur naturally. Moderate full-body summer sun exposure induces production of 10,000-25,000 IU, and if this were a daily habit, sun exposure is equivalent to about 5,000 IU/day.
Still, it’s amazing that such a small dose and rise in 25(OH)D can still find statically significant results in blood pressure. There have been a few vitamin D and blood pressure randomized controlled trials now. It would be nice to see a meta-analysis of these randomized controlled trials to see what all of them combined have to say.