Although it does not have a clear, direct impact on long-term BP, the avoidance of exposure to cigarette smoke is a critical aspect of cardiovas- cular risk reduction but as yet there are no RCTs in the CKD population. Dietary supplementation. The effects of potassium sup- plementation on BP have been assessed in a number of These have produced conflicting results, with some but not all indicating a benefit. CKD patients often have reduced capacity for potassium excretion, particularly as the GFR falls, such that the risk of hyperkalemia may be increased. In the absence of specific studies demonstrating a benefit in CKD patients, we cannot recommend potassium supplementation to reduce BP in patients with CKD. The evidence base for magnesium supplementation is similar, with some but not all studies suggesting a benefit with respect to BP.53,73 Although hypermagnesemia is not a common problem in CKD patients, magnesium supplemen- tation cannot be recommended without specific data demonstrating its safety and efficacy. Fish-oil supplementation has been shown to produce small but significant reductions in BP in a number of RCTs and systematic reviews.53,74 The mechanisms of these effects remain uncertain, however and the safety of fish oil has not been clearly demonstrated in CKD patients. Although some data supporting the use of fish oil exists for patients with IgA it is premature to recommend this treatment for BP lowering in the CKD population. BP-LOWERING AGENTS RCTs involving both CKD and non-CKD populations in which a target BP has been set at the levels recommended in this Guideline clearly show that most patients will require two or more antihypertensive agents to achieve these targets. Surveys of BP control in CKD patients indicate that three or more agents are frequently needed. 