Alzheimer’s. A diabetic disorder of the brain?

Did you know Alzheimer’s disease and other forms of dementia are now the second leading cause of death in Australia and the first in the U.K.?

Some may believe that cognitive decline is inevitable for most, especially as we grow older. Sure, some people are predisposed to increased risk of developing dementia or Alzheimer’s disease, but research is finding there are other factors that can potentiate the onset.

Cognitive decline and blood sugar

Dementia is a collection of symptoms affecting behaviour, thinking, and ability to perform everyday tasks, and has no known cure. Alzheimer’s disease (AD) is one cause of dementia, a neurodegenerative disease characterised by symptoms such as memory loss, easily disorientated, lack of logical thinking, and the presence of beta-amyloid plaque and neurofibrillary tangles in the brain cells.

Despite on-going researching efforts, the cause of AD remains somewhat elusive. However, there is a possible connection between high blood glucose in poorly managed type 2 diabetes or insulin resistance with reduced hippocampal volume, cognitive impairment and AD.^1-2

Type 2 diabetes is a progressive condition presenting in high blood glucose due to insulin resistance, ineffective insulin action, reduced insulin output by the pancreas, or a combination of any of these three. One has increased risk of developing type 2 diabetes through a combination of factors, including poor diet, lack of exercise, and genetic and familial predisposition, and it is associated with obesity and high blood pressure.

It is good to differentiate type 2 diabetes from type 1 diabetes, which is an autoimmune condition affecting the function of the insulin producing beta-cells of the pancreas, and unlike type 2 diabetes, is not linked to modifiable diet and lifestyle factors.

So, the link between type 2 diabetes and brain function? Scientists have recently found due to impairment in insulin signalling in the brain, brain cells are just not getting the glucose they need to function and perform complex tasks such as forming memories.¹

Insulin signalling dysfunction and resistance in the brain make less glucose available to be metabolised by brain cells for energy, regardless of high circulating levels of blood glucose. This can impact memory and cognition.³

In fact, recent research out of Japan has drawn a parallel between insulin signalling function of the pancreas and that of the brain, concluding that Alzheimer’s disease can be described as a diabetic disorder of the brain.³ The researchers also found when insulin signalling improved there were decreases in blood glucose that correlated with improved memory.³

The similar mechanism identified in the pancreas and the brain has gotten scientists excited about potential new treatment.

However, that is in the future! For now, what can we do to help manage insulin resistance in the noggin and boost cognitive function?

Eating for memory

Consuming copious amounts of added sugar has been associated with the development of type 2 diabetes (especially sugar-sweetened beverages). And too much of the sweet stuff is thought to hasten production of beta-amyloid plaques and cognitive decline,^4-5 as with a Western style diet that is typically high in trans-fat, processed foods, and refined sugars.

Research has found eating a diet high in these foods can put us and even our kids at risk of learning, mood, and memory difficulties, which may in part be due to a reduction of a protein called reelin. Low reelin levels are associated with eating poorly and Alzheimer’s.⁶

Such outcomes are not surprising. The Western highly-processed-high-sugar-high-nasty-fat diet is pro-inflammatory. This causes inhibition of growth of new brain nerve tissue, impacting hippocampal function and volume.^5;7-8

So perhaps by eating well, we can stabilise blood glucose levels, lower inflammation, and reduce the risk of hurting our hippocampus.

A Mediterranean style diet jammed with whole foods including vegetables, fruit, and healthy fats like olive oil, nuts, seeds and oily fish is naturally anti-inflammatory and has been correlated with decreased plaques and neurofibrillary protein tangles that are typically found in the brains of those with Alzheimer’s disease and cognitive decline.⁹

And a recent study has found swapping out junk for real whole foods can increase insulin sensitivity in the hippocampus.¹⁰ 

See where we are going with this? Eat good food, your brain will salute you a thumbs up. Eat not-so-good food, your brain will likely sad face.

While diet may not be the only factor involved in insulin resistance or memory loss, it sure as heck can play a critical role in increasing or decreasing risk.

What to do?

Show your brain some love by:

• Eating your veg
  In general, loading your plate with veg whenever you can is going to be good for overall health.
  Phytonutrients lutein and zeaxanthin, found in orange and leafy green vegetables like sweet potato and kale, may help the brain work more efficiently. ¹¹ Sulforaphane, a phytoconstituent found in brassica veg like broccoli has been found to encourage brain cell health, differentiation, & growth.¹²
• Enjoying healthy fats
  Eating good fats over any old fat is worth the distinction. Choose whole food fat foods that will nourish – not punish – your brain. Food rich in omega-3 fatty acids – like walnuts, flaxseed, chia seed, leafy greens and oily fish – is brain protective, & may even reverse insulin signalling dysfunction that resulted from a diet high in free sugars like fructose.⁴ 
• Limiting intake of heavily refined and processed foods, high in added sugar, and trans-fatty acids
  As mentioned above, eating high amounts of added sugar and free fructose has been correlated with decreased hippocampal volume, cognitive decline & increased beta-amyloid production. And a diet high in ‘fatty’ foods – the hydrogenated fats like the stuff you get from fast food takeaway and heavily processed packaged goods like pastry, biscuits and the like – have been correlated with later life mood and cognition issues.⁶
• Getting regular exercise, being social, and sleeping deeply – all may help reduce the risk for memory loss.

By Angela Johnson (BHSc Nut. Med.)

Please note: If you have any concerns with your diet, lifestyle, risk for type 2 diabetes and/or cognitive function, please do visit your trusted healthcare practitioner, who can work with you and your individual situation to help you be in your best possible state of health.

References:

1. Kim, D, Yu, JH, Shin, M, Shin, Y, & Kim, M 2016, ‘Hyperglycemia Reduces Efficiency of Brain Networks in Subjects with Type 2 Diabetes’, PLoS ONE, vol. 11, no. 6, pp. 1-14.
2. Willette, AA, Bendlin, BB, Starks, EJ, Birdsill, AC, Johnson, SC, Christian, BT, Okonkwo, OC, La Rue, A, Hermann, BP, Koscik, RL, Jonaitis, EM, Sager, MA, & Asthana, S 2015, ‘Association of Insulin Resistance With Cerebral Glucose Uptake in Late Middle-Aged Adults at Risk for Alzheimer Disease’, JAMA Neurology, vol. 72, no. 9, pp. 1013-1020.
3. Moriguchi, S, Ishizuka, T, Yabuki, Y, Shioda, N, Sasaki, Y, Tagashira, H, Yawo, H, Yeh, JZ, Sakagami, H, Narahashi, T, & Fukunaga, K 2016, ‘Blockade of the KATP channel Kir6.2 by memantine represents a novel mechanism relevant to Alzheimer’s disease therapy’, Molecular Psychiatry, [Epub ahead of print].
4. Agrawal, R, & Gomez-Pinilla, F 2012, ”Metabolic syndrome’ in the brain: deficiency in omega-3 fatty acid exacerbates dysfunctions in insulin receptor signalling and cognition’, The Journal Of Physiology, vol. 590, no. 10, pp. 2485-2499.
5. Barnes, JN, & Joyner, MJ 2012, ‘Sugar highs and lows: the impact of diet on cognitive function’, The Journal Of Physiology, vol. 590, no. 12, p. 2831
6. Labouesse, MA, Lassalle, O, Richetto, J, Iafrati, J, Weber-Stadlbauer, U, Notter, T, Gschwind, T, Pujadas, L, Soriano, E, Reichelt, AC, Labouesse, C, Langhans, W, Chavis, P, & Meyer, U 2016, ‘Hypervulnerability of the adolescent prefrontal cortex to nutritional stress via reelin deficiency’, Molecular Psychiatry, [Epub ahead of print].
7. Jacka, FN, Cherbuin, N, Anstey, KJ, Sachdev, P, & Butterworth, P 2015, ‘Western diet is associated with a smaller hippocampus: a longitudinal investigation’,BMC Medicine, vol. 13, no. 1, pp. 1-8
8. Molteni R, Barnard RJ, Ying Z, Roberts CK, Gomez-Pinilla F. A high-fat, refined sugar diet reduces hippocampal brain-derived neurotrophic factor, neuronal plasticity, and learning. Neuroscience. 2002;112:803–14
9. Merrill, DA Siddarth, P Raji, CA Emerson, ND Rueda, F Ercoli, LM Miller, KJ Lavretsky, H Harris, LM Burggren, AC Bookheimer, SY Barrio, JR & Small, GW 2016, ‘Modifiable Risk Factors and Brain Positron Emission Tomography Measures of Amyloid and Tau in Nondemented Adults with Memory Complaints’, American Journal of Geriatric Psychiatry, [Epub ahead of print].
10. Sims-Robinson, C, Bakeman, A, Bruno, E, Jackson, S, Glasser, R, Murphy, GG, & Feldman, EL 2016, ‘Dietary Reversal Ameliorates Short- and Long-Term Memory Deficits Induced by High-fat Diet Early in Life’, PLoS ONE, vol. 11, no. 9, pp. 1-16.
11. Lindbergh, CA, Mewborn, CM, Hammond, BR, Renzi-Hammond, LM, Curran-Celentano, JM, & Miller, LS 2016, ‘Relationship of Lutein and Zeaxanthin Levels to Neurocognitive Functioning: An fMRI Study of Older Adults’, Journal Of The International Neuropsychological Society: JINS, pp. 1-12.
12. Kim, J, Lee, S, Choi, B, Yang, H, Hwang, Y, Park, JY, LaFerla, FM, Han, J, Lee, KW, & Kim, J 2016, ‘Sulforaphane epigenetically enhances neuronal BDNF expression and TrkB signaling pathwaysffig’, Molecular Nutrition & Food Research.