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.