Do statins contribute to dementia?

Question

A documentary, Cholesterol, the Great Bluff (2016) - IMDb (depending upon location, available in Cholesterol: The Great Bluff), contains many examples of why statins are not only useless, but are actually harmful.

It claims that statins have severe side effects, the worst perhaps simply being that they do exactly what they are intended to do, reduce cholesterol. The problem is that a significant portion of the brain is composed of cholesterol, and the destruction of that cholesterol can cause dementia.

A (badly formatted) transcript, Transcript: Cholesterol: The Great Bluff | TVO.org, contains this anecdote, for instance:

[A woman in her forties with long brown hair speaks.]

[A caption reads "Doctor Beatrice Golomb, Professor of Medicine."]

[Doctor Golomb says]

We published a case series of 171 people with cognitive adverse effects on statins. And some of these are quite compelling and troubling cases. There was one individual who was a retired professor in multiple different departments with a reported IQ of over 180 who had actually been identified by two academic institutions as having the rapidly progressive form of Alzheimer's disease. And he actually went to a 50-year school reunion with a sign around his neck saying, "My name is [….] I have Alzheimer's", so that people would understand why he would repeat the same sentence again and again and wouldn't recognize people he'd known closely for decades. He also couldn't read more than a page of text because he couldn't remember what he'd read. And then his wife decided to stop his Simvastatin and he appeared to screen for an experimental drug trial for Alzheimer's at another university. And they reassessed him. And they said, not only do you not have Alzheimer's — you don't have dementia. And by his reckoning it was about two years before he was all the way back to normal. But by then he was back to reading three newspapers a day. The New York Times, the Wall Street Journal and Washington Post online.

Beatrice Golomb is Professor in Residence, Medicine, at UCSD.

The same source quotes Michel de Lorgeril — Wikipédia, doctor and researcher at CNRS, The European Society of Cardiology:

Statins, and anti-cholesterol drugs in general, cross over the blood-brain barrier, which means they enter the brain and disturb the production of cholesterol within the brain. This has an awful secondary effect because no one was aware of it until recently, and due to pressure from certain doctors and toxicologists, the health authorities finally admitted that statins could cause memory problems, sleep disorders and therefore neuro-toxicity. Unfortunately, despite being a major toxic factor, its effects are still underestimated. We must not forget that Alzheimer’s disease starts with memory problems, sleep disorders and therefore you can say that statins - although additional studies would obviously be required... almost push us towards Alzheimer’s disease, especially since statins are diabetogenics and diabetes is a major risk factor for developing Alzheimer’s, some people even say that Alzheimer’s is a type-3 diabetes.

This documentary finds many problems with current practices and beliefs related to cholesterol, but I'm not asking about the documentary itself, or about the significance of blood cholesterol.

Restricting the question to the very believable claim that statins cause brain damage and are responsible for recent increases in the incidence of dementia, something the pharmaceutical industry would obviously dispute, has there been any research to refute this specific claim?

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EDIT:

In a comment, Dave Sherohman provides two references to small studies, one supporting (107 subjects) and one refuting (55 subjects) this claim. In both cases, the subjects all had type 1 diabetes. For the purposes of this question, I'll quote only the one supporting it:

Statin use and cognitive function in middle-aged adults with type 1 diabetes

RESULTS
… Propensity score analyses support that associations between poor cognitive outcomes and statin use were not due merely to confounding by indication.

CONCLUSION
Statin use was associated with cognitive impairment, particularly affecting memory, in these middle-aged adults with childhood-onset T1D, whom at this age, should not yet manifest age-related memory deficits.
…
Core tip: Animal and cell culture studies show that statins can damage cerebral gray and white matter, thereby affecting cognitive function. Findings from human studies remain controversial; early observational studies reported that statin use negatively affected cognition, especially memory, while more recent studies have not replicated these findings. Even though statins are widely prescribed for people with type 1 diabetes (T1D), only one study to date has examined whether statin use is related to cognitive impairment in this patient population. We propose that deleterious effects statins may exert on cognition may be more pronounced in people with T1D, as these individuals are already at an increased risk of cognitive impairment due to long-term exposure to metabolic dysregulation.

Answer 1

Statins for or against dementia? Irrelevant. So: no in both ways.

Statins seem to have both benefits and detriments. There are a few side effects of notable gravity. While most conventional practitioners emphasise the harm reduction potential and health benefits, downplaying the side-effects that even have to be listed in the packaging, the so-called 'cholesterol-skeptics' play the same game with diametrically opposed aims from the other side of the table.

This claim about increased risk for dementia it is from one of those cholesterol skeptics. In this case the reasoning given is broad, unspecific and abstract instead of based on at least a detailed theory.

The interesting part here is that individual studies from statin-enthusiasts claimed just the opposite: "Statins are great for reducing dementia!"

That is handled in by Chochrane as:

There was no significant difference in behaviour, global function or activities of daily living in the statin and placebo groups. We assessed risk of bias as low for all studies. We found no studies assessing role of statins in treatment of VaD.

Analyses from the studies available, including two large randomised controlled trials, indicate that statins have no benefit on the primary outcome measures of ADAS‐Cog or MMSE.
–– Statins for the treatment of dementia

And

We included two trials with 26,340 participants aged 40 to 82 years of whom 11,610 were aged 70 or older. All participants had a history of, or risk factors for, vascular disease. The studies used different statins (simvastatin and pravastatin). Mean follow‐up was 3.2 years in one study and five years in one study. The risk of bias was low. Only one study reported on the incidence of dementia (20,536 participants, 31 cases in each group; odds ratio (OR) 1.00, 95% confidence interval (CI) 0.61 to 1.65, moderate quality evidence, downgraded due to imprecision). Both studies assessed cognitive function, but at different times using different scales, so we judged the results unsuitable for a meta‐analysis. There were no differences between statin and placebo groups on five different cognitive tests (high quality evidence). Rates of treatment discontinuation due to non‐fatal adverse events were less than 5% in both studies and there was no difference between statin and placebo groups in the risk of withdrawal due to adverse events (26,340 participants, 2 studies, OR 0.94, 95% CI 0.83 to 1.05).

There is good evidence that statins given in late life to people at risk of vascular disease do not prevent cognitive decline or dementia. Biologically, it seems feasible that statins could prevent dementia due to their role in cholesterol reduction and initial evidence from observational studies was very promising. However, indication bias may have been a factor in these studies and the evidence from subsequent RCTs has been negative. There were limitations in the included studies involving the cognitive assessments used and the inclusion of participants at moderate to high vascular risk only.
–– Statins for the prevention of dementia

As well as reagarding stopping statin treatment

We found no evidence to enable us to make an informed decision about statin withdrawal in dementia. Randomised controlled studies need to be conducted to assess cognitive and other effects of statins in participants with dementia, especially when the disease is advanced.
–– Statin withdrawal in people with dementia

So, systematic reviews cannot confirm what statin enthusiasts claim for preventing dementia with statins. The 'why' for this sorry state of concrete evidence is then exemplified when looking at the direction this claim was making

This case report is consistent with recent literature that fails to demonstrate an association between statins and cognitive impairment. It also provides support for the practitioner to prescribe and continue statins without fear of precipitating or worsening cognitive impairment.
–– Downs TN.: "Statins: The Burglar of Memory?", Consult Pharm. 2018 Dec 1;33(12):706-710. doi: 10.4140/TCP.n.2018.706..

While the above is anecdotal, the gist seems to be just about right. Statins are neither cure-alls nor entirely harmless, dosage has to be calibrated tightly, but for analysing dementia alone:

Does statin use cause memory decline in the elderly?

Further, reports that statin therapy might be protective against Alzheimer's disease have subsequently been refuted in randomized trials. Low-level evidence based on case reports suggests that statins may adversely affect memory, a significant consumer concern. In this review, the published evidence on statins and memory in the elderly in randomized controlled trials and prospective observational cohort studies was examined in detail. Overall, there was moderate-strength evidence that statin therapy did not increase the risk of dementia in the elderly and low-strength evidence for no increased risk for Alzheimer's disease. Further, there was moderate-strength evidence that statin therapy in the elderly did not increase the risk for mild cognitive impairment or worsen global cognitive performance in the cognitively intact or impaired. There was moderate-strength evidence for no deterioration of memory function in the elderly. On balance, there was a moderate level of evidence of neither harm nor benefit on memory; however, the published literature contains a number of deficiencies that are detailed in this review, not limited to selection biases and deficiencies of detailed testing.
–– Samaras K & Brodaty H & Sachdev PS: "Does statin use cause memory decline in the elderly?", Trends Cardiovasc Med. 2016 Aug;26(6):550-65. doi: 10.1016/j.tcm.2016.03.009.