caffeine’s effects on cardiovascular system
Caffeine levels peak 30-120 minutes after oral intake and caffeine's half-life is 3-6 hours.  Acute caffeine intake has been shown to significantly increase central blood pressure as well as systolic and diastolic blood pressure. Drinking coffee, within three hours, causes a measurable rise in both systolic and diastolic blood pressure, and that effect can persist even into the following day. In people prone to hypertension, drinking coffee may be harmful. The amount of caffeine in two to three cups of coffee can raise systolic pressure 3 to 15 millimeters of mercury (mm Hg) and diastolic pressure 4 to 13 mm Hg in people without high blood pressure.  Typically, blood pressure changes occur within 30 minutes, peak in 1-2 hours, and may persist for more than 4 hours.
Coffee is a main source of caffeine in take. Coffee drinking is shown to be a predictor for the incidence of heart palpitations. This is due to its effects on raising cortisol, it increases heart rate. It is also implicated in the potential to produce cardiac arrhythmias. Apart from that caffeine and coffee each appear to increase risk of coronary heart disease. A lower risk of coronary heart disease among moderate coffee drinkers might be due to antioxidants found in coffee.  The increased risk of coronary heart disease may have connections with which the action of caffeine on increasing serum cholesterol level.
Heavy coffee consumption has been shown to increase the short-term risk of heart attack, or acute myocardial infarction.  The more coffee consumed, the greater the risk. Epidemiological study looking at heart attacks and risk factors has shown that coffee drinking increases the risk of succumbing to an acute myocardial infarction in people with diabetes. Researchers have found that caffeine is detoxified in the liver at a slower or faster rate depending on a certain gene. The population is roughly split in half between fast and slow metabolisms for caffeine. Caffeine is metabolized by the enzyme CYP1A2, which has a fast and a slow variant. People homozygous for the fast variant (1A) metabolize caffeine faster than people carrying the slow variant (1F). For people who are genetically slow to metabolize caffeine, drinking coffee significantly raises the risk of developing a heart attack, or experiencing a myocardial infarction. The relative risk of myocardial infarction in the hour after coffee intake was 1.49. Occasional coffee drinkers (< or =1 cup/day) had a relative risk of myocardial infarction of 4.14, moderate coffee drinkers (2-3 cups/day) had a relative risk of 1.60 and heavy coffee drinkers (> or =4 cups/day) had a relative risk of 1.06. 
Among people who don't consume caffeine on a regular basis, caffeine can cause a temporary but sharp rise in blood pressure. Exactly what causes this spike in blood pressure is uncertain. Some experiments suggest that caffeine narrows blood vessels by blocking the effects of adenosine, a hormone that helps keep them widened. Caffeine may also stimulate the adrenal gland to release more cortisol and adrenaline, which cause your blood pressure to increase. Some researches have found that people who regularly drink caffeine have a higher average blood pressure than those who drink none. Experiments have suggested that regular consumers of caffeine develop a tolerance to it and as a result, caffeine doesn't have a long term effect on their blood pressure.
Caffeine has been demonstrated to negatively affect stiffness in the aorta as well as the wave reflections and aortic pressure, in healthy adults as well as in adults with hypertension. Both radial and aortic systolic, diastolic and pulse pressure increased significantly by caffeine. Increased arterial stiffness is a contributing factor in coronary artery disease and is involved in the process of arteriosclerosis or hardening of the arteries. [7, 8]
Caffeine intake is linked to higher levels of serum cholesterol, with particularly high levels noted in people who drink boiled coffee or coffee processed at high temperatures. Other forms of coffee have also been shown to increase serum cholesterol levels including decaffeinated coffee, and studies show that replacement of regular coffee with decaffeinated coffee does not affect lipid levels. After adjusting for age and adiposity, the mean serum cholesterol level was 11 mg/dl higher for women consuming 200 mg or more of caffeine per day compared with those consuming less. The relative risk of high serum cholesterol (> 260 mg/dl) was greater than 2 for women consuming 200 mg or more of caffeine per day. A significant positive interaction between smoking and caffeine consumption in their association with serum cholesterol levels has found for females.  But some experiments suggest that associations of caffeine and beverage intakes with cholesterol, triglycerides, high-density lipoprotein cholesterol, and high-density lipoprotein2 cholesterol were also inconsistent and there is little or no association of caffeine with lipoproteins or with blood pressure in healthy young adults. 
Coffee drinking is associated with decreased absorption of magnesium resulting in lower blood levels of magnesium. Caffeine reduces the reabsorption of calcium and magnesium in the kidney, causing minerals to be excreted in the urine. Magnesium is an essential mineral utilized in more than 300 enzymatic reactions and physiological processes including energy metabolism, effective utilization of glucose, hormonal balance and proper heart function. Calcium too is a very important mineral that perform many important functions in the body. Such as mediators of hormone actions, in blood coagulation, in maintaining skeletal system, to maintain ion balance across the cell membranes and in muscle contraction etc. So it will leads to many problems with excretion of these minerals with diuretic caused by caffeine intake.
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