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Kidney Function in Patients with Diabetic Nephropathy Linked to Seasonal BP

Posted: Sunday, October 10, 2010

Researchers say clinicians should consider seasonal variations in systolic blood pressure when treating patients with diabetic nephropathy, after finding seasonal variations in urinary albumin-to-creatinine ratio (UACR), likely linked to blood-pressure changes.

The investigators noted that blood pressure has been seen to increase in winter, compared with summer, and some reports have shown a seasonal change in glycemic control and the onset of diabetes. However, until this study, it was not known whether kidney function in patients with diabetic nephropathy varied with the season in relation to blood pressure.

The study recruited 430 patients (275 male, 155 female, mean age 65) with Type 2 diabetes, early nephropathy, and microalbuminuria. Subjects visited the clinic regularly every three months, and data were collected at every visit from 2006 to 2009. Microalbuminuria was defined by a UACR of 30 to 300 mg of urinary albumin to 1 g of creatinine. Patients with an advanced stage of nephropathy with increased creatinine were excluded from the study.

When fluctuations in UACR were grouped by seasons, the researchers found "significant seasonal variations in the [UACR], systolic blood pressure, and [glycated hemoglobin] HbA1c," Wada said. The UACR was highest in the winter, as was systolic blood pressure. In contrast, HbA1c peaked in spring. Estimated glomerular filtration rate (eGFR) and diastolic blood pressure showed no significant seasonal variations.

Seasonal variation in clinical parameters related to diabetic nephropathy with microalbuminuria

Measurement	Highest season	Lowest season			p
UACR (mg/g creatinine)	Winter, 72.8+4.4	Summer, 54.6+3.4	0.002
Systolic blood pressure (mm Hg)	Winter, 136+0.68			Summer, 133+0.68	<0.001
HbA_1c (%)	Spring, 7.39+0.03	Fall, 7.15+0.03	<0.001

There was a significant correlation between systolic blood pressure and UACR (p=0.05, r=0.79), with UACR rising with increased systolic pressure. The researchers observed no correlation between blood pressure and HbA1c or between HbA1c and UACR.

The fact that both UACR and systolic blood pressure were highest in winter and lowest in summer suggests that the seasonal change in systolic blood pressure … may contribute to the variations in UACR, something also seen in earlier studies.

It was suggested that the variations seen might be related to seasonal changes in serum vitamin-D levels, and exercise which was not looked at.

Source: http://www.diabetesincontrol.com/index.php?option=com_content&view=article&id=9904&catid=53&Itemid=8, Wada Y, Hamamoto Y, Iwasaki Y, et al. Seasonal variations of urinary albumin/creatinine ratio in subjects with Type 2 diabetes and nephropathy. European Association for the Study of Diabetes 2010 Meeting; September 23, 2010; Stockholm, Sweden Abstract 1214.