Cognitive disorder and dementia in type 2 diabetes mellitus

Table 1 Type 2 diabetes mellitus and its complications

Major complications of diabetes
Macrovascular (large artery damage)
Ischaemic heart disease
Cerebrovascular disease
Microvascular (peripheral neuropathy and damage to the small vessels)
Retinopathy: Retinal microaneurysm and retinal detachment
Nephropathy: Altered of renal function with microalbuminuria, proteinuria, and progression to chronic renal failure
Neuropathy

Table 2 Difference between vascular dementia, Alzheimer dementia, and mixed dementia

	Characteristics
Vascular dementia	Cerebral vascular network involving veins, arteries, capillaries.Clinical presentation is more variable
Alzheimer dementia	Caused by the death of nerve cells (neurons) in certain selected areas of the brain. Characteristic abnormalities (neuritic plaques and neurofibrillary tangles)
	Memory impairment at initial clinical presentation.
Mixed dementia	Vascular disease + Alzheimer's disease

Table 3 Summary of studies relating diabetes and Alzheimer's disease

Ref.	Study	n	Conclusion
Ott et al[33], 1999	Prospective population-based cohort	6370 older adults	Diabetes mellitus almost doubled the risk of dementia. Patients treated with insulin were at highest risk of dementia
Luchsinger et al[34], 2005	Longitudinal	1138 older adults	Four risk factors (diabetes, hypertension, heart disease, and current smoking) were associated with a higher risk of AD. The risk of AD increased with the number of vascular risk factors. Diabetes and current smoking were the strongest risk factors
Xu et al[38], 2009	Population-based cohort study	1248 dementia-free cohort	Uncontrolled diabetes increases the risk of Alzheimer's disease and VD. Their findings suggest a direct link between glucose dysregulation and neurodegeneration
Wang et al[36], 2012	Population-based cohort study	615529 diabetic patients; 614871 random controls	Diabetes may increase the risk of AD in both sexes and all ages
Tolppanen et al[40], 2013	Case-Control study	3012 diabetic patients; 3372 AD	Individuals with clinically verified AD are more likely to have a history of clinically verified and medically treated diabetes than the general aged population, although the difference is small
Huang et al[37], 2014	Population-based cohort study	1000000 random controls; 71433 diabetic patients	Newly diagnosed DM was associated with an increased risk of AD. The use of hypoglycemic agents did not ameliorate the risk
Gudala et al[35], 2013	Meta-analysis	28 studies	The results showed a 73% increased risk of all type of demetia, 56% increase of AD, and 127% increase of VD in diabetes patients
Biessels et al[19], 2006	Meta-analysis	14 studies	There is convincing evidence that shows an increased risk of dementia in people with diabetes. The risk factors and mechanisms that drive the association between diabetes and accelerated cognitive decline and dementia need to be identified before adequate treatment measures can be developed
Cheng et al[41], 2012	Meta-analysis	19 studies	Diabetes was a risk factor for incident dementia (including AD, VD, and any dementia) and MCI
Zhang et al[42], 2017	Meta-analysis	17 studies	The risk of AD is higher among people with diabetes than in the general population

DM: Diabetes mellitus; AD: Alzheimer’s disease; VD: Vascular dementia; MCI: Mild cognitive impairment.