Abstract:
Iodineisessentialforthyroidhormonesynthesis.Excessiveconsumptionof
goitrogenicfoodslikesoybeans(GlycinemaxLinnaeus)andcassava(Manihot
esculenta Crantz)which are staple foods in WestAfrica can resultin
hypothyroidism.Increasediodineconsumptionwasproposedtoameliorate
deleterious effects of goitrogenic foods on the thyroid but excessive
consumptioncanleadtohyperthyroidism andhypothyroidism whichalters
glucosehomeostasis.Thereishowever,limitedinformationontheeffectof
excessiveiodineandgoitrogenicfoodcombinationonglucosehomeostasis.
Therefore,thisstudywasdesignedtoinvestigatetherolesofexcessiodineand
concurrentgoitrogenicfoodintakeonthyroidfunctionandglucosehomeostasis
inrats.
Cassavatuberswerepeeled,grated,fermentedandroasted.Soybeanseeds
wereboiled,dehulledandsun-dried.Sixtymalerats(90-120g)weredivided
intothreegroups(n=20);1(StandardRatFeed(SRF),2(30%soybeans)and3
(30%cassava).Eachofthethreegroupsconsistedoffoursubgroups(n=5);A
(Non-diabeticwithoutiodine),B (Non-diabetic+iodine),C (Diabeticwithout
iodine)andD(Diabetic+iodine).10mgofiodine/kgoffeedwasadministered.
The rats were fed ad libitum according to theirgroups throughoutthe
experiment.Diabetes mellitus was induced with intraperitonealalloxan
monohydrate(150mg/kg)after6weeksoffeedingandtheratswerefedfor
twomoreweeks.Onthelastdayoftheexperiment,oralglucose(1.75g/kg)
wasadministeredandglucosetolerancewasassessedusingglucoseoxidase
method.InsulinresistancewasmeasuredbyHomeostaticModelAssessment
ofInsulinResistance(HOMA-IR).Serum triodothyronine(T3),thyroxine(T4),
Thyroid Stimulating Hormone (TSH),thyroglobulin and thyroperoxidase
antibodiesandfastinginsulinlevelswereassessedusingELISA.Datawere
analysedusingdescriptivestatisticsandANOVAatα0.05.
IndiabeticratsfedwithSRF,iodineintakeincreasedbloodglucoselevelsafter
30minutes(386.67±7.74vs496.83±5.73mg/dL),60minutes(332.00±3.47vs
495.83±4.27mg/dL),90minutes(352.17±3.51vs428.83±10.66mg/dL)and
120minutes(342.83±6.33vs447.00±4.66mg/dL)ofglucoseingestion.Innon
-diabetic rats fed with 30% soybeans,iodine treatmentincreased blood
glucose levels after120 minutes ofglucose ingestion (99.67±1.98 vs
114.00±3.41mg/dL).Iodineconsumptionincreasedfastingbloodglucose
levelsindiabeticratsfedwith30% cassava(279.83±8.73vs304.50±5.38
mg/dL).Consumptionof30%soybeanscausedincreasedbloodglucoselevels
indiabeticrats(342.83±6.35vs412.17±10.11mg/dL)butlowerbloodglucose
vi
levelswereobservedwithconsumptionof30% cassava(347.83±6.35vs
279.83±8.73mg/dL).Cassavaintakecausedinsulinresistance(4.8)indiabetic
rats.Iodineintakeloweredinsulinlevelsinnon-diabeticratsfedwithSRF
(1.48±0.16vs0.45±0.09IU/mL)andcassava(5.63±0.03vs0.43±0.17IU/mL).
IndiabeticratsfedwithSRF,iodinetreatmentreducedT4andincreasedTSH
concentrations(T4: 11.75±0.21 vs6.75±0.22 mg/dL,TSH:2.28±0.08 vs
3.08±0.15 IU/mL).Intake of30% soybeans increased serum T3 levels
(2.98±0.26vs6.75±0.06ng/mL)andconcurrentiodinetreatmentloweredT3
levels(6.75±0.06vs2.90±0.91ng/mL)innon-diabeticrats.Thyroglobulinand
thyroperoxidaseantibodieswereabsentinalltherats.
Consumptionofgoitrogenicfoods;soybeansandcassavawithexcessiodine
causedhyperglycaemiaandsuppressedthyroidfunctioninwistarrats.
