Vitamin D may lower blood pressure, but the effect is at most modest and the evidence is not consistent. Thus, while there are obvious health benefits from getting enough vitamin D, either from exposure to sunlight, from diet or from dietary supplements, you should not think of vitamin D as a treatment or partial treatment for high blood pressure.
Significance
Blood pressure results, measured by your doctor or nurse from putting a cuff on your upper arm, are presented as two numbers: systolic and diastolic blood pressure, abbreviated as SBP and DBP. Normal is less than 120 and less than 80, respectively. Elevated blood pressure, often referred to as hypertension, affects about 50 million adults in the U.S. Consequences include increased risk of heart disease, stroke and kidney disease. Prehypertension is defined as SBP 120-139 or DBP 80-89. Stage I hypertension is defined as SBP 140-159 or DBP 90-99. Stage 2 hypertension is defined as SBP greater than 160 or DBP greater than 100. Drug treatments are recommended for Stage I and II hypertension. Lifestyle changes such as weigh loss can be combined with drug treatments for greater effect.
Population Studies
According to Dr. M.I. Ullah's 2010 article in the "International Journal of Endocrinology," when large groups of people are tested, those with low blood levels of vitamin D are more likely to be hypertensive. Similarly, researchers who recruit healthy populations into multi-year studies find that those who had low vitamin D at the start were at greater risk of becoming hypertensive by the end of the study. These results were true for the majority but not all of published studies.
Clinical Trials
While population studies appeared promising, clinical trials in which patients with hypertension were given vitamin D are less convincing. In the October 2009 issue of "Journal of Hypertension," Dr. Witham pooled the results from eight published clinical trials. On average, SBP decreased by 3.6 and DBP decreased by 3.1. The authors concluded this was weak evidence in support of a beneficial effect on blood pressure. A weakness here is that the vitamin D dose used in the clinical trials may have been too low to have an impact.
Theories/Speculation
Dr. Ullah discussed several possible mechanisms by which vitamin D could affect blood pressure. He proposed that excess fluid could be retained in blood because low vitamin D led to a rise in renin and/or parathyroid hormones. Vitamin D may be needed to maintain artery flexibility. Ullah also touches on theories that vitamin D may not be directly responsible for managing blood pressure. Obesity and older age both result in elevated blood pressure and low vitamin D. By this way of thinking, low vitamin D occurs in the same people as hypertension, but the first is not causing the second.
Warning
The National Institutes of Health recommendations for lifestyle changes to help control hypertension do not include increasing vitamin D intake. Your doctor has a wide range of effective blood pressure lowering drugs to choose from, with known safety profiles. Currently, the safe upper limit for recommended intake of vitamin D is 4,000 IU per day. Higher doses have been tied to side effects such as nausea, loss of appetite and vomiting. Prolonged use of very high doses is implicated in damage to arteries and kidneys.
References
- National Institutes of Health: Seventh Report on Prevention, Detection, Evaluation and Treatment of High Blood Pressure
- "International Journal of Endocrinology": Does vitamin D deficiency cause hypertension? Current evidence from clinical studies and potential mechanisms; Ullah 2010
- PubMed.gov: Effect of vitamin D on blood pressure: a systematic review and meta-analysis
