Research proposal: Vitamin D, an antihypertensive agonist? The aim of this study therefore is to explore the effect of Vitamin D as an antihypertensive agonist. In addition, it would investigate any difference between supplemental vitamin D and dietary vi

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Research proposal: Vitamin D, an antihypertensive agonist?

Nadine El Halabi

Rima kaddoura

Mohammad Kobrosly

Fall 2010-2011

Nursing 406

American University of Beirut

According to the American Heart Association, the estimated percentage of people suffering from hypertension in the United States is 33.3% (AHA, 2009). Meanwhile, a study conducted in Lebanon in 2005 revealed that 23.1% of the Lebanese population suffers from hypertension. The prevalence of this disease is increasing annually in association with the increase of cardiovascular risk factors (obesity, smoking, high fat diet, diabetes... etc.). Therefore, a lot of studies have been conducted in order to improve the continuous care and to promote awareness for those people who are at a high risk for developing hypertension.

On the other hand, vitamin D deficiency is very common in today’s Lebanese population with a study revealing that 85 % of postmenopausal osteoporotic women are vitamin d deficient (Yared, 2009) . Vitamin D is known to have an effect on renal and cardiovascular functions (Li, 2003). Therefore it is directed towards the same target as antihypertensive medications. As a matter of fact, vitamin D has receptors in the kidneys that alter the renin-angiotensin system which has a direct effect on controlling blood pressure (Li, 2003). It may be used from several sources, which include: environmental sources (i.e the sun), dietary sources (cod liver oil, salmon, tuna…etc), and vitamin D pills (National institutes of health, 2009). As a result, with hypertension being this prevalent and with the availability of vitamin D and its similarity to antihypertensive medications in terms of effect, a relation may be found between vitamin D, antihypertensive medications, and hypertension.

Aim of the study

The aim of this study therefore is to explore the effect of Vitamin D as an antihypertensive agonist. In addition, it would investigate any difference between supplemental vitamin D and dietary vitamin D as antihypertensive agonists.

Research questions

In order to be able to achieve the proposed research aim, several questions have to be answered:

  1. Does vitamin D have the same mechanism as antihypertensive medications on lowering blood pressure?
  2. Is there a difference in the antihypertensive effects between the different sources of vitamin D (supplemental and dietary)?

Hypotheses

Several hypotheses emerge:

1st hypothesis: Vitamin D is expected to improve blood pressure maintenance in patients on antihypertensive

2nd hypothesis: Knowing that vitamin D availability is limited in dietary products, supplemental vitamin D is expected to be a better antihypertensive agonist than that from dietary intake.

Literature review

Vitamin D has been found to have receptors on the blood vessels and on the heart itself  (Li, 2003). Therefore, Vitamin D exerts some kind of effect on these two elements of the cardiovascular system. However, this effect has not been fully researched, and studies that have in fact investigated this relationship have shown contradictory evidence. Some researchers claim that it is beneficial for the cardiovascular system (Wang, 2009), while others decline these findings (Margolis, 2008). In terms of cardiovascular diseases, hypertension is one of the most prevailing and it is globally widespread (AHA, 2009). In addition, hypertension needs constant management and requires different lifestyle changes from patients. It was therefore suggested by researchers that the intake of vitamin D should be included in one of these lifestyle changes if found that it does in fact decrease blood pressure (Jorde, 2000).

Blood pressure is the measurement of the force of blood as it passes through the arteries (Li, 2003). It depends on many factors, including the diameter of the arteries, the length of the arteries, and the viscosity of the blood. The borderline for hypertension (high blood pressure) is 140/90 mmHg (with 140 systolic pressure and 90 diastolic pressure).

Hypertension may be primary or secondary (to diseases such as: disorders of the adrenal glands, kidney diseases, thyroid and parathyroid problems…etc). Risk factors for primary hypertension include insulin resistance, obesity, and sensitivity to sodium, increased renin activity, genetics, and more. Recently, some studies have shown that Vitamin D deficiency is also a risk factor for primary hypertension (Wang, 2008). As a matter of fact Vitamin D has an effect on the renin-angiotensin system. It decreases the amount of renin release and as a result decreases blood pressure (Li, 2003).

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On the other hand, where does our intake of Vitamin D come from? The most obvious source of Vitamin D is sun exposure. However, this may be limited in some areas and with people who stay indoors most of the time. Another source is dietary intake; some of the foods that contain noteworthy amounts of Vitamin D include Milk, Salmon, Tuna, and Eggs (National institutes of health, 2009). Finally, the last possible source of Vitamin D is supplements which are becoming more and more available (National institutes of health, 2009).

The findings that linked Vitamin D deficiency and primary hypertension ...

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