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Microalbuminuria has been associated with non-dipping of nocturnal blood pressure (BP) in people with type 2 diabetes, but the mechanism of this association is unclear. We aimed to identify the development of microalbuminuria in patients with nocturnal non-dipping of BP and type 2 diabetes. Data were examined from 150 people with type 2 diabetes who had undergone ambulatory BP monitoring, non-dippers were defined as those with a systolic nocturnal BP dip less than 10% of the daytime BP.
The development of microalbuminuria, over five years of follow-up, in dippers and non-dippers was not significantly different. Non-dippers who were microalbuminuric at baseline were more likely to have a higher body mass index (p = 0.01) and to be male (p <0.01).
This lack of a difference may be due to the initial exclusion of microalbuminuric patients, who may be genetically predetermined to develop microalbuminuria. Further prospective trials are required to investigate this relationship.
More than 50% of patients with type 2 diabetes have hypertension, and overall the presence of type 2 diabetes is associated with a two to three-fold increased risk of cardiovascular disease. Ambulatory BP has been shown to be a better predictor of cardiovascular mortality than a clinic measurement and also allows the assessment of the presence or absence of the normal nocturnal dip in BP.
It is well recognised that BP is higher through the day and dips by approximately 20% through the night. A nocturnal dip of <10% of the daytime average SBP is described as non-dipping. The incidence of non-dipping amongst patients with diabetes is around 50%, in comparison with an incidence of non-dipping of 10% in essential hypertension, and a non-dipping profile is associated with increased cardiovascular risk.
The causes of non-dipping are unclear, suggestions have included variation in activity levels during the day, quality of sleep, the presence of autonomic dysfunction and renal impairment. Studies of hypertensive subjects with and without diabetes have demonstrated a significant relationship between nocturnal non-dipping of BP and urinary albumin excretion. We have previously demonstrated type 2 diabetes that non-dipping is associated with macrovascular disease, nephropathy and increasing age. However, the temporal relationship between non-dipping and the subsequent development of microalbuminuria, remains unknown, i.e. does microalbuminuria precede non-dipping or vice versa? Alternatively there may be a common aetiological factor in the development of both non-dipping and microalbuminuria. This study was designed to determine whether non-dipping in normoalbuminuric patients was associated with an increase in the development of albuminuria over a five-year period.
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