Calcium deficiency may cause high blood pressure, and this may be treated with supplements.
Sodium chloride is often blamed as a causative factor in cases of high blood pressure. However, the evidence does not support a role for salt in causing high blood pressure in healthy individuals. Excess salt consumption tends to result in increased salt excretion thus maintaining homeostasis and extracellular fluid volume. However, salt may play a contributory role in raising the blood pressure of those with particular salt sensitivity. For example, increased dietary salt has been shown to raise the blood pressure of adults born prematurely. The role of calcium in blood pressure regulation has been largely ignored by mainstream medicine and few people are aware of the possible blood pressure lowering effects of calcium. Calcium intake shows an inverse association with blood pressure in humans, but the complexity of dietary nutrient intakes make the cause and effects of the relationship difficult to determine. For example, the Western diet is high in sodium but low in calcium, which makes the causative agent in blood pressure difficult to determine.
In this regard epidemiological studies can be misleading as determining the cause and effects of nutrient physiological interactions is difficult. Many epidemiological studies rely on food questionnaires and dietary recall sheets that are known to be unreliable in some circumstances. Therefore direct assessment of the nutrient intake of subjects in clinical trials is more appropriate. Calcium supplementation in clinical trials has been performed and the findings support a blood pressure lowering effect for dietary calcium. For example, in one study1 researchers supplemented subjects with 500 mg per day of calcium or a placebo tablet. Compliance of the supplementation protocol was monitored throughout. The results showed that there was no effects of the calcium supplements on the blood pressure of normotensive subjects. However, those subjects with hypertension had reductions in systolic blood pressure of 13 mm Hg over 4 years, while the unsupplemented group had an increase of 7 mmHg over the same time period.
Therefore calcium does not lower blood pressure except in those with hypertension. The association between calcium and body weight is well reported and both dairy and calcium are known to cause weight loss effects in human trial. Therefore the blood pressure lowering effects of calcium might relate to its ability to lower body weight. The authors did not measure the body weights of the subjects but the study length (4 years) suggests that the calcium supplements could have caused moderate weight loss in this time. Other studies have shown blood pressure lowering effects for calcium supplements in double blind clinical trials over shorter time periods (here). Those who respond to calcium supplements with reduced blood pressure tend to have elevated plasma parathyroid hormone and low plasma levels of calcium2. This suggest that the blood pressure lowering effects of calcium may be a response to a calcium deficient or calcium insufficient state and that calcium replenishment reverses this condition.
