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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 31, No 1, January/February 2020
AFRICA
5
Cardiovascular Topics
A cross-sectional cohort study with microvascular
complications in patients with type 2 diabetes with and
without hypothyroidism
Louise Johnson, Brian Rayner
Abstract
Objectives:
Previous reports have suggested an association
between hypothyroidism and macrovascular complications in
type 2 diabetes (T2DM) but the association with microvascular
complications is not well documented. This study aimed to deter-
mine whether there were significant differences in these complica-
tions in patients with T2DM with and without hypothyroidism.
Methods:
This was a retrospective, cross-sectional, case–
control study from a single centre specialising in diabetes
in South Africa. T2DM was defined by American Diabetes
Association criteria. The cases were all patients treated for
hypothyroidism and the controls were clinically and biochemi-
cally confirmed euthyroid, who were under follow up between
1 January and 1 July 2016. Chronic kidney disease (CKD) was
defined as an estimated glomerular filtration rate (eGFR) of
<
60 ml/min, determined by the CKD-epidemiology collabo-
ration equation (CKD-EPI) and/or albumin/creatinine ratio
>
3 mg/mmol. Diabetic retinopathy (DR) was defined as the
presence of aneurysms, bleeds, exudates and new vessel forma-
tion on the retina examined by an ophthalmologist. Diabetic
peripheral neuropathy (DPN) was defined as the presence of
symptoms, loss of 128-Hz sensation and abnormal 10-gm
monofilament. Cardiovascular disease (CVD) was defined as
the presence of major adverse cardiovascular events (MACE).
Results:
There were 148 cases and 162 controls. Compared
to the controls, the cases were older (65.6 vs 59.4 years,
p
<
0.00001), more likely to be female (67.6 vs 39.5%,
p
<
0.0001)
and white (89.2 vs 79.6%,
p
=
0.02), have a lower HbA
1c
level
(7.5 vs 8.2%,
p
=
0.0001), eGFR (64.4 vs 72.7 ml/min,
p
=
0.0006) and triglyceride level (2.18 vs 2.55 mmol/l,
p
=
0.04),
have a higher high-density lipoprotein cholesterol level (1.13
vs 1.02 mmol/l,
p
=
0.001), a longer duration of diabetes (14.8
vs 11.6 years,
p
=
0.001) and using fewer antidiabetic agents
(1.82 vs 2.19,
p
=
0.001). There was a higher prevalence of
CKD (44 vs 57.8%,
p
=
0.03) and CVD (59.3 vs 45.3,
p
=
0.06), and a trend towards higher DR (66.7 vs 47.6,
p
=
0.09).
There was no difference in body mass index, hypertension,
low-density lipoprotein cholesterol level (all patients received
statin therapy), DPN and amputations. After adjusting for
confounding factors, there was no association between CKD
and DR, and hypothyroidism, but the trend to association
with CVD persisted (OR 1.97.
p
=
0.07).
Conclusions:
Hypothyroidism in T2DM was not associated
with microvascular disease after adjusting for confounding
factors. There was a nearly two-fold risk of CVD. The study
is limited by the retrospective and observational design.
Keywords:
hypothyroidism, type 2 diabetes, microvascular and
macrovascular complications
Submitted 28/3/19, accepted 20/6/19
Published online 2/8/19
Cardiovasc J Afr
2020;
31
: 5–8
www.cvja.co.zaDOI: 10.5830/CVJA-2019-036
The National Health and Nutritional Examination Survey III
showed a prevalence of overt and subclinical hypothyroidism
(SCH) of 0.3 and 4.3%, respectively.
1
Insulin resistance, type 2
diabetes mellitus (T2DM) and hypothyroidism are reported to
occur more commonly than by chance, although the exact aetiology
is uncertain.
2
Both T2DM and hypothyroidism are associated with
cardiovascular disease (CVD), often through complex mechanisms,
and the concurrence of hypothyroidism and diabetes may further
amplify endothelial dysfunction, insulin resistance, poorer diabetic
control and microvascular complications.
3
In a systematic review and meta-analysis of SCH in T2DM,
the prevalence was 10.2%, and T2DMwas associated with a 1.93-
fold increase in risk for SCH. Furthermore, SCH was associated
with an overall odds ratio of 1.74 for diabetic nephropathy, 1.42
for diabetic retinopathy (DR), 1.85 for peripheral arterial disease,
and 1.87 for diabetic peripheral neuropathy (DPN).
4
However
data from individual studies have not always been consistent
with these associations.
5,6
Given the paucity of data and the contradictory findings of
studies, we aimed to investigate the association of T2DM and
hypothyroidism with micro- and macrovascular complications
in South Africa.
Methods
This was a retrospective, observational, cross-sectional study
of patients with T2DM performed in a large private practice
Montana Hospital, Pretoria, South Africa
Louise Johnson, MB ChB, FCP, MMed, MSc
Division of Nephrology and Hypertension, and Kidney and
Hypertension Research Unit, University of Cape Town,
South Africa
Brian Rayner, MB ChB, FCP, MMed, PhD,
brian.rayner@uct.ac.za