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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 31, No 1, January/February 2020
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AFRICA
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.
11
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 single-
centre 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.
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.
References
1.
Hollowell JG, Staehling NW, Flanders WD, Hannon WH, Gunter EW,
Spencer CA,
et al.
Serum TSH, T(4), and thyroid antibodies in the
United States population (1988 to 1994): National Health and Nutrition
Examination Survey (NHANES III).
J Clin Endocrinol Metab
2002;
87
(2): 489–499.
2.
Diez JJ, Iglesias P. An analysis of the relative risk for hypothyroidism
in patients with Type 2 diabetes.
Diabetic Med
2012;
29
(12): 1510–1514.
3.
Kadiyala R, Peter R, Okosieme OE. Thyroid dysfunction in patients
with diabetes: clinical implications and screening strategies.
Int J Clin
Pract
2010;
64
(8): 1130–1139.
4.
Han C, He X, Xia X, Li Y, Shi X, Shan Z,
et al
. Subclinical hypothyroid-
ism and type 2 diabetes: a systematic review and meta–analysis.
PLoS
One
2015;
10
(8): e0135233.
5.
Kim BY, Kim CH, Jung CH, Mok JO, Suh KI, Kang SK. Association
between subclinical hypothyroidism and severe diabetic retinopathy
in Korean patients with type 2 diabetes.
Endocrine J
2011;
58
(12):
1065–1070.
6.
Qi Q, Zhang QM, Li CJ, Dong RN, Li JJ, Shi JY,
et al
. Association of
thyroid-stimulating hormone levels with microvascular complications in
type 2 diabetes patients.
Med Sci Monitor
2017;
23
: 2715–2720.
7.
American Diabetes Association. 2. Classification and Diagnosis of
Diabetes: Standards of Medical Care in Diabetes – 2018.
Diabetes Care
2018;
41
(Suppl 1): S13–S27.
8.
Vanderpump MP, Tunbridge WM, French JM, Appleton D, Bates D,
Clark F,
et al.
The incidence of thyroid disorders in the community: a
twenty-year follow-up of the Whickham Survey.
Clin Endocrinol
1995;
43
(1): 55–68.
9.
Moon S, Kim MJ, Yu JM, Yoo HJ, Park YJ. Subclinical hypothyroidism
and the risk of cardiovascular disease and all-cause mortality: a meta-
analysis of prospective cohort studies.
Thyroid
2018;
28
(9): 1101–1110.
10. Seo C, Kim S, Lee M, Cha MU, Kim H, Park S,
et al.
Thyroid hormone
replacement reduces the risk of cardiovascular diseases in diabetic
nephropathy patients with subclinical hypothyroidism.
Endocrine Pract
2018;
24
(3): 265–272.
11. Harada PHN, Buring JE, Cook NR, Cobble ME, Kulkarni KR, Mora
S. Impact of subclinical hypothyroidism on cardiometabolic biomarkers
in women.
J Endocrine Soc
2017;
1
(2): 113–123.
12. Prieto-Almeida F, Panveloski-Costa AC, Crunfli F, da Silva Teixeira S,
Nunes MT, Torrao AS. Thyroid hormone improves insulin signaling and
reduces the activation of neurodegenerative pathway in the hippocam-
pus of diabetic adult male rats.
Life Sci
2018;
192
: 253–258.
13. Pandrc MS, Ristic A, Kostovski V, Stankovic M, Antic V, Milin-Lazovic
J,
et al.
The effect of early substitution of subclinical hypothyroidism on
biochemical blood parameters and the quality of life.
J Med Biochem
2017;
36
(2): 127–136.