To me at least, it seems that links between low-level radiation exposure and Alzheimer's disease are tenuous at best. You can look at the painkiller theory of Alzheimer's for an example of finding correlations with rising levels of dementia that are unlikely to involve causation, but where one can dig up biochemistry that looks somewhat supportive to the idea. Yet in comparison to the standard view, that has very little weight of evidence. Suggestions that greater exposure to low levels of ionizing radiation, via medical scanning procedures and air travel, contributes meaningfully to dementia seems like another example of the type. If anything, the weight of evidence on low-level radiation exposure indicates that it produces beneficial hormetic effects that should modestly slow the progression of aging. But again, it is possible to produce results that look somewhat supportive of the thesis, as here. I am skeptical on the whole, and would want to see a lot more evidence before abandoning the more mainstream view that rising Alzheimer's incidence is a consequence of demographic aging and rising rates of obesity in the population at large.
Alzheimer's disease is the leading cause for dementia in the elderly, and its global prevalence is supposed to increase dramatically in the following decade - up to 80 million patients by 2040. In a new study, researchers show that low doses of ionising radiation induce molecular changes in the brain that resemble the pathologies of Alzheimer's. Large numbers of people of all age groups are increasingly exposed to ionizing radiation from various sources. Many receive chronic occupational exposure from nuclear technologies or airline travel. The use of medical diagnostics and therapeutic radiology has increased rapidly - for example more than 62 million CT scans per year are currently carried out in USA. Approximately one third of all diagnostic CT examinations are scans of the head region. "All these kinds of exposures are low dose and as long as we talk about one or a few exposures in a lifetime I do not see cause for concern. What concerns me is that modern people may be exposed several times in their lifetime and that we don't know enough about the consequences of accumulated doses."
Recent data suggest that even relatively low radiation doses, similar to those received from a few CT scans, could trigger molecular changes associated with cognitive dysfunction. In their new study, the researchers have elucidated molecular alterations in the hippocampus of mice. The hippocampus is an important brain region responsible for learning and memory formation and it is known to be negatively affected in Alzheimer´s. The authors induced changes in the hippocampus by two kinds of chronic low-dose-rate ionizing radiation treatments. The mice were exposed to cumulative doses of 0.3 Gy or 6.0 Gy given at low dose rates of 1 mGy over 24 hours or 20 mGy over 24 hours for 300 days. "Both dose rates are capable of inducing molecular features that are reminiscent of those found in the Alzheimer's disease neuropathology. When you compare these figures you will find that we exposed the mice to a more than 1000 times smaller cumulative dose than what a patient gets from a single CT scan in the same time interval. And even then we could see changes in the synapses within the hippocampus that resemble Alzheimer´s pathology." According to the researchers, the data indicate that chronic low-dose-rate radiation targets the integration of newborn neurons in existing synaptic wires.