They discovered that adults in the study who were moderately deficient in vitamin D had a 53 per cent increased risk of developing dementia
I hate articles like this. They state an increased risk as a percentage but never tell you what the initial risk was.
If the risk of getting dementia is .0001 to begin with than a 53% increase is still very small.
this study found that people with very low vitamin D levels were more than twice as likely to develop any kind of dementia.
How likely were they to develop dementia in the first place?
From the article
Dementia is one of the greatest challenges of our time, with 44 million cases worldwide – a number expected to triple by 2050 as a result of rapid population aging. A billion people worldwide are thought to have low vitamin D levels and many older adults may experience poorer health as a result.
I don’t have hard numbers, but I can extrapolate from the above. Start with earths population of about 7 billion. Say that those at an age susceptible to dementia make up the oldest 20% of the population, which gives 1.4 billion. Assuming all those 44 million are of that 1.4 billion, that’s 44/1400 = 0.0314, or 3.14%. 3 out of 100. My guess of 20% may be off, and the 44 million likely includes younger cases as well, but it’s close enough to show it’s not a negligible risk.
Edit: Looking at world age distribution, 20% oldest is an age of 50-55 and older.