The SA Journal Diabetes & Vascular Disease Volume 16 No 2 (November 2019)

RESEARCH ARTICLE

SA JOURNAL OF DIABETES & VASCULAR DISEASE

VOLUME 16 NUMBER 2 • NOVEMBER 2019

The increased prevalence of hypothyroidism in women in this

study probably reflects underlying gender differences, previously

reported.

1,8

Similarly, the increased age in the cases probably reflects

the higher prevalence in older people.

The lower prevalence of

hypothyroidism in black people was also reported in previous

studies,

but our results need to be interpreted with caution in view

of the skewed nature of the population.

Hypothyroidism has previously been reported in a systematic

review and meta-analysis to be associated with microvascular

complications that included DR, DKD and DPN. Although on

univariate analysis, an association with DKD was demonstrated,

this was not confirmed on multivariate analysis. The most

important predictor of microvascular complications in our study

was found to be increasing age, especially in relation to DKD and

DPN. Unfortunately only 24.2% of our subjects went for formal

retinal examination and this could have masked an association

between DR due to a type 1 statistical error.

The relationship between hypothyroidism, including SCH and

CVD, has been well established,

and treatment with thyroxine

may reduce this risk.

In our study there was a trend for increased

CVD in both univariate and multivariate analysis. The reason for

not showing a clear association with CVD was probably mitigated

by the fact that all the cases received thyroxine and statins to

control LDL cholesterol. There was no difference in LDL cholesterol

between the cases and controls as a result. Raised LDL cholesterol

due to hypothyroidism is probably one of the major mechanisms

for CVD.

An interesting finding in this study was that hypothyroid

cases had improved glycaemic control, used less hypoglycaemic

medication, and had higher HDL cholesterol and lower triglyceride

levels. This is suggestive of reduced insulin resistance, which is

contrary to reports in the literature.

It is possible that because all

cases received thyroxine to control T4 and TSH levels, there was

reversal of the insulin resistance that contributed to developing

T2DM. Improvement in insulin resistance with thyroxine has been

reported in experimental models and humans.

12,13

The major limitation of this study was that it was a singlecentre

study, and sample size was not calculated. The negative

findings may be due to inadequate statistical power of the

study. Although we attempted to control for confounders, this

does not completely negate the effect of confounders on the

micro- and macrovascular outcomes. Furthermore, the patients

with hypothyroidism were adequately treated and therefore

biochemically euthyroid, thus negating the potential negative

micro- and macrovascular consequences of hypothyroidism. The

retinopathy group had a limited sample size due to many subjects

not attending their ophthalmological examination. This limits the

conclusions regarding the association of hypothyroidism and DR.

Conclusions

In this retrospective, observational study, a link between

hypothyroidism and SCH and diabetic microvascular complications

was not found, but there was a nearly two-fold risk for CVD. Cases

also demonstrated improved glycaemic control despite fewer

antidiabetic drugs, and indirect evidence for less insulin resistance

than the controls with T2DM. These findings warrant further study

for confirmation.

Acknowledgements

We thank Katherine Manning for doing the statistical analysis, and

Marna Pieterse, Annalize van der Heever and Charles Loots for

collecting the data from the patient files and entering them into

the Excel spreadsheet.

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