better to diuretic therapy than drugs that interfere with the renin–angiotensin system. High renin levels predispose to hypertension by causing sodium retention through the following mechanism: Increased renin → Increased angiotensin II → Increased vasoconstriction, thirst/ADH and aldosterone → Increased sodium reabsorption in the kidneys (DCT and CD) → Increased blood pressure. Diabetes Hypertension can also be caused by Insulin resistance and/or hyperinsulinemia, which are components of syndrome X, or the metabolic syndrome. Insulin is a polypeptide hormone secreted by cells in the islets of Langerhans, which are contained throughout the pancreas. Its main purpose is to regulate the levels of glucose in the body antagonistically with glucagon through negative feedback loops. Insulin also exhibits vasodilatory properties. In normotensive individuals, insulin may stimulate sympathetic activity without elevating mean arterial pressure. However, in more extreme conditions such as that of the metabolic syndrome, the increased sympathetic neural activity may over-ride the vasodilatory effects of insulin. Recent studies claim that obesity is a risk factor for hypertension because of activation of the renin–angiotensin system (RAS) in adipose tissue, and also linked renin–angiotensin system with insulin resistance, and claims that any one can cause the other. Smoking Smoking does not directly cause high blood pressure. However it is a known risk factor for other serious cardiovascular disease. Vitamin deficiency It has been suggested that vitamin D deficiency is associated with cardiovascular risk factors. It has been observed that individuals with a vitamin D deficiency have higher systolic and diastolic blood pressures than average. Vitamin D inhibits renin secretion and its activity, it therefore acts as a "negative endocrine regulator of the renin–angiotensin system". Hence, a deficiency in vitamin D leads to an increase in renin secretion. This is one possible mechanism of explaining the observed link between hypertension and vitamin D levels in the blood plasma. Also, some authorities claim that potassium might both prevent and treat hypertension. Lack of exercise Regular physical exercise reduces blood pressure. The UK National Health Service advises 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic activity per week to help prevent hypertension. Pathophysiology Cardiac output and peripheral resistance are the two determinants of arterial pressure and so blood pressure is normally dependent on the balance between cardiac output and peripheral resistance. Cardiac output is determined by stroke volume and heart rate; stroke volume is related to myocardial contractility and to the size of the vascular