Several risk factors may lead to a stroke. These include high blood pressure, obesity, high cholesterol levels, narrowed arteries, diabetes, arrhythmia, and a previous stroke or family history of strokes. A lack of exercise, poor diet, smoking, and drinking more than two alcoholic beverages per day may contribute to enhanced risk. High blood pressure is the leading risk factor for strokes because it leads to plaque formation, restricting blood flow. Smoking is the leading preventable risk factor because it decreases oxygen in the blood, weakens blood vessel walls, and can decrease good cholesterol.