Being overweight and/or obese can cause high blood pressure in a variety of ways. When there is increased weight it takes more pressure to move the blood around the body. When the weight gain is in the abdominal area there is a greater risk for high blood pressure because this type of fat is more likely to cause the arteries to become thick and stiff. When the pipes (the blood vessels) get stiff it is harder to push the blood through. When it gets hard to move blood around the body there is an increase in adrenalin. This will increase salt retention and further increase blood pressure.
Obesity is associated with sleep apnea and diabetes, which both carry an ncreased risk of high blood pressure.
The good news is that when you lose weight (even a small amount) the blood pressure can go down and the blood vessels can lose their stiffness. In addition, diabetes and sleep apnea can improve. The key is to eat healthy and exercise to prevent the complications of being overweight.