Changes in Body Functions Researchers continue to study how various changes in normal body functions cause high blood pressure. The key functions affected in high blood pressure include -  kidney fluid and salt balances  -  the renin-angiotensin-aldosterone system   - the sympathetic nervous system activity   - blood vessel structure and function. kidney fluid and salt balances the renin-angiotensin-aldosterone system the sympathetic nervous system activity blood vessel structure and function. Kidney Fluid and Salt Balances The kidneys normally regulate the bodys salt balance by retaining sodium and water and eliminating potassium. Imbalances in this kidney function can expand blood volumes, which can cause high blood pressure. Renin-Angiotensin-Aldosterone System The renin-angiotensin-aldosterone system makes angiotensin and aldosterone hormones. Angiotensin narrows or constricts blood vessels, which can lead to an increase in blood pressure. Aldosterone controls how the kidneys balance fluid and salt levels. Increased aldosterone levels or activity may change this kidney function, leading to increased blood volumes and high blood pressure. Sympathetic Nervous System Activity The sympathetic nervous system has important functions in blood pressure regulation, including heart rate, blood pressure, and breathing rate. Researchers are investigating whether imbalances in this system cause high blood pressure. Blood Vessel Structure and Function Changes in the structure and function of small and large arteries may contribute to high blood pressure. The angiotensin pathway and the immune system may stiffen small and large arteries, which can affect blood pressure. Genetic Causes High blood pressure often runs in families. Years of research have identified many genes and other mutations associated with high blood pressure. However, known genetic factors only account for 2 to 3 percent of all cases. Emerging research suggests that certain DNA changes before birth also may cause the development of high blood pressure later in life. Unhealthy Lifestyle Habits Unhealthy lifestyle habits can cause high blood pressure, including - high sodium intake and sodium sensitivity  - drinking too much alcohol  - lack of physical activity. high sodium intake and sodium sensitivity drinking too much alcohol lack of physical activity. Overweight and Obesity Research studies show that being overweight or obese can increase the resistance in the blood vessels, causing the heart to work harder and leading to high blood pressure. Medicines Prescription medicines such as asthma or hormone therapies (including birth control pills and estrogen) and over-the-counter medicines such as cold relief medicines may cause high blood pressure. This happens because medicines can - change the way your body controls fluid and salt balances  - cause your blood vessels to constrict  -  impact the renin-angiotensin-aldosterone system, leading to high blood pressure.  change the way your body controls fluid and salt balances cause your blood vessels to constrict impact the renin-angiotensin-aldosterone system, leading to high blood pressure. Other Causes Other causes of high blood pressure include medical conditions such as chronic kidney disease, sleep apnea, thyroid problems, or certain tumors. These conditions can change the way your body controls fluids, sodium, and hormones in your blood, which leads to secondary high blood pressure.