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The regulation of cellular calcium metabolism is central to blood pressure homeostasis; the higher the level of cytosolic free calcium, the greater the smooth muscle vasoconstrictor tone, the catecholamine secretion, the sympathetic nervous system activity, and thus blood pressure. An increase of cellular calcium, as part of the final common pathway leading to vascular smooth muscle contraction, may directly explain the increased peripheral resistance characteristic of essential hypertension. Animal, clinical and some epidemi-ological evidence suggests that high blood pressure is associated with abnormalities of calcium metabolism and secondary activation of the parathyroid gland.4,25 30

Hypertension

The effect of calcium dietary modifications on blood pressure control has generated great controversy. There are considerable epidemiological and clinical trial data on the relationship between blood pressure levels and calcium intake.31 Epidemiologically, a consistent inverse relationship has been observed between dietary calcium intake and blood pressure. The epidemiological relationship of dietary calcium to blood pressure was definitely assessed by McCarron, who reanalyzed the data of the National Health and Nutrition Examination Survey (NHANES), observing an inverse relationship of calcium intake to blood pressure,32,33 suggesting that a dietary calcium 'deficiency' may contribute to elevation of blood pressure in humans. The reanalysis of the NHANES data by McCarron indicated that a dietary calcium intake of at least 1000 mg was associated with a 40-50% reduction in hypertension prevalence.33 Following this observation, a number of experimental and observational studies have supported the hypothesis that calcium supplementation can reduce blood pressure.34 39

However, it should be emphasized that almost 80 years before the NHANES results, W. Addison first suggested a link of dietary calcium to clinical hypertension. He reported that oral calcium supplementation could lower blood pressure in hypertensive individuals.34 The findings of Addison were ignored for more than 50 years until similar results were reported in rats by Ayachi,35 in normotensive humans by Belizan etal.36 and in human hypertensives by others.31,37 39 The results of randomized controlled trials of calcium supplementation on blood pressure have not been uniform. Pooled analyses showed a small but statistically significant reduction in systolic blood pressure and a non-significant trend toward reduction in diastolic blood pressure.40 42

The non-uniform results of the calcium supplementation trials performed has led some investigators to hypothesize that only a subgroup of individuals respond to calcium supplementation. Resnick etal. have proposed that the calcium supplementation was more beneficial among low-renin, salt-dependent forms of hypertension (around 30% of all hypertensive individuals). Those subjects exhibiting a more hypotensive response to calcium supplementation were also those that were more responsive to salt restriction (salt-volume-dependent hypertension).43 Thus, the effect of calcium in lowering blood pressure is related and synergistic to the restriction of salt, in the subgroup of responsive subjects (salt-sensitive hypertension). A role for calcium-regulating hormones, 1,25 vitamin D and PTH in mediating both the hypertensive effect of salt and the hypotensive action of increased calcium intake was also sug-gested.43,44 In particular, the beneficial effect of calcium supplementation may be mediated by a suppression of PTH secretion and reduction of circulating levels. St John et al.45 have showed a weak, but significant, relationship between blood pressure and calcitropic hormones in a group of elderly people, suggesting that bigger changes in systolic blood pressure, may be observed in older subjects with an underlying hypovitaminosis D associated with elevated PTH levels.

The recently published Dietary Approaches to Stop Hypertension (DASH) trial has provided outcome data for hypertension control and dietary patterns rich in dairy products, fruits, vegetables, grains and lean meat. The dietary pattern reached in the DASH diet reflects the intake of these foods at the levels considered appropriate, but rarely achieved in the Western diet.46

Additional information is needed to identify sub-populations in a state of calcium deficiency that may benefit more from calcium supplementation. In particular, as previously discussed, elderly people may require greater calcium intake due to calcium malabsorption and vitamin D deficiency,1,11,12 and old age is also a period associated with an increased risk of elevated blood

pressure.

Although the modest response in systolic and diastolic blood pressure reduction found in the trials does not justify the use of calcium supplementation as a sole treatment for patients with mild hypertension, a recommendation for increased calcium intake or calcium supplementation may be a useful advisory to be added to the other non-pharmacological suggestions for prevention and treatment of hypertension, at least in subjects with low-renin, salt-sensitive hypertension, and in special population more at risk of calcium deficiency, such as elderly hypertensives and women with gestational hypertension.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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