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Effects of exogenous human insulin dose adjustment on body mass index in adult patients with type 1 diabetes mellitus at Kalafong Hospital, Pretoria, South Africa, 2009 - 2014
Abstract
Background. To maintain fasting blood glucose levels within near to the normal range in type 1 diabetes mellitus (DM), frequent insulin dose adjustments may be required with short-, intermediate- and long-acting insulin formulations. Patients on human insulin generally experience weight gain over time, regardless of the level of glycaemic control achieved.
Objectives. To determine the effects of human insulin, adjusted quarterly to achieve glycaemic control, on body mass index (BMI), and establish dose regimens that achieve optimal glycaemic control without increasing BMI in patients with type 1 DM at the Kalafong Diabetes Clinic in Pretoria, South Africa.
Methods. The sample size (N=211, 48.8% male) was obtained by non-probability convenience sampling of all available records of patients with type 1 DM aged ≥18 years at baseline at the clinic. The longitudinal relationships of covariates with time-varying BMI, as well as with time-varying glycated haemoglobin (HbA1c) levels, were explored using multilevel mixed-effects linear regression modelling.
Results. The majority of the patients (84.8%) received the twice-daily biphasic human insulin regimen and the remainder received the basal neutral protamine Hagedorn (NPH) plus prandial regular human insulin regimen. The multivariable multilevel mixed-effects linear regression model indicated that time-varying BMI was significantly positively related to time-varying twice-daily biphasic insulin dosage (β (standard error) 0.464 (0.190), p=0.015), baseline HbA1c (0.092 (0.026), p<0.001) and baseline BMI (0.976 (0.016), p<0.001). There were significant inverse associations with the number of years spent in the study (–0.108 (0.052), p=0.038), time-varying HbA1c (–0.154 (0.031), p<0.001) and male sex (–0.783 (0.163), p<0.001). There were non-significant negative longitudinal associations of age (–0.005 (0.006), p=0.427) and current smoking status (–0.231 (0.218), p=0.290) with BMI outcomes.
Conclusions. There was no evidence that optimal quarterly-prescribed daily dosage adjustments of insulin improved and maintained blood glucose control without increasing body weight. When compared with the basal NPH plus prandial insulin regimen, twice-daily biphasic insulin was associated with a statistically significant increase in subsequent BMI. Baseline HbA1c and BMI were also significantly positively associated with time-varying BMI. However, males appeared to be at a lower risk than females of an increase in BMI during insulin therapy. A question for further research is whether the analogue insulins will be associated with the same increase in BMI, as well as the same modest improvements in HbA1c, seen in this sample.
