Smoking tobacco is bad for your circulatory health. in an attempt to maintain the blood's capacity to deliver oxygen, the body increases its red blood cell production, and this increases the viscosity of the blood. in addition, nicotine from tobacco causes arteries to constrict. for a nonsmoker, with blood viscosity of 2.5×10−3pa⋅s, normal blood flow requires a pressure difference of 8.0 mm of hg between the two ends of an artery. if this person were to smoke regularly, his blood viscosity would increase to 2.7×10−3pa⋅s, and the arterial diameter would constrict to 90 % of its normal value.