A recent paper published in the journal Neurology shows that, for patients with a history of Alzheimer’s disease (but, interestingly, not vascular dementia), the risk of cancer was reduced. And for patients with a history of cancer, their risk of Alzheimer’s disease was reduced. If their risk profiles demonstrate this level of dependence, what ties them together?
Assume two things are true (which is certainly a big assumption as there is preliminary evidence accompanied by unanswered questions for both):
- Cancer is, in some way, shape or form, promoted by chronically elevated blood sugar.
- Alzheimer’s is, in some way, shape or form, a consequence of chronic neural uptake of high levels of glucose from the bloodstream and/or the dysregulation of inflammation caused by chronically elevated insulin levels.
Then this trade off in disease risk begins to make sense. On a diet high in sugar, the body begins to react by decreasing sensitivity to insulin in muscle tissue (normally a prime consumer of blood glucose). Neural tissue and the tissues in the eyes, however, do not have the luxury of insulin resistance (as they use a different glucose transporter) and maintain their uptake of very high levels of glucose. This is likely why Type II diabetics often struggle with diabetic retinopathy and neuropathy.
Just how high a level of glucose uptake is maintained is probably quite individual. In people whose neural tissues can absorb large quantities of sugar from the bloodstream, total blood sugar may remain near ‘normal’ but the neural tissue is forced to deal with high concentrations of glucose and the resulting metabolic by-products. Long term, this struggle may lead to Alzheimer’s disease.
In individuals whose neural tissue accepts glucose uptake at a lower level, blood sugar stays elevated and the resulting diffusion of glucose throughout the body likely results in global intercellular glucose levels higher than in those individuals with high neural glucose uptake. If sugar concentrations really do contribute to cancer, globally elevated tissue glucose (which, to my knowledge, isn’t routinely measured) would be an excellent way to stack the deck in favor of cancer, i.e. should a cell lose control of its growth process, in a high-sugar environment it would grow like mad.
We measure gross capacity for uptake of blood glucose (without regard to where it goes) via the usual oral glucose tolerance test but there’s currently no way to assess an individual’s neural glucose uptake capacity. And given that the options are Alzheimer’s or cancer, I’ll choose to just avoid sugar intake whenever possible.