The subtitle would make much more sense (and would not be misleading as it now stands) if the author had added just one word. The current subtitle makes one expect to read an article about how some vitamin found in the blood is somehow either CAUSING dementia, or is otherwise somehow linked to dementia.  However, after you read the article, the opposite meaning  becomes evident, that would have been clarified by the addition of the word, "DEFICIENT:"  

            A TECHNIQUE for detecting Improvised Explosive Devices (IEDs) is being used
            to identify vitamins DEFICIENT in the bloodstream linked to dementia.

So, this article is really about how a vitamin B 12 DEFICIENCY is what is being linked to dementia! That is a very different thing than what is implied by the subtitle, that a particular vitamin  found in the blood is linked to dementia!  

It has been known for many decades that a vitamin B12 deficiency can actually cause a form of dementia with symptoms that are hard indeed to distinguish from other varied causes of dementia, but which can been diagnosed with a simple blood test for vitamin B12 levels. This type of dementia, caused by a  Vitamin B 12 DEFICIENCY, may be totally reversible if caught early enough, with simple Vitamin B12 injections  (best supported by a good overall potent Vitamin B complex supplement in addition).  Vitamin B12 is a large, complex molecule that can become difficult to impossible to absorb properly from the digestive tract from food or oral supplements because of a variety of reasons: lack of sufficient   hydrochloric acid secreted by the stomach, lack of a substance labeled as "intrinsic factor," also secreted by the stomach in healthy people, certain medications, such as metformin used by millions of people to treat their diabetes, can cause a B12 deficiency as a side effect,  avoidance of animal foods by vegetarians and vegans, while not taking B12 supplements  to make up for the total lack of B12 in almost plant foods, etc.  Since B12 is totally non-toxic at even very high levels, it is a "no-brainer" for anyone with memory issues  to at least try supplementing with  a high dose  oral  or nasal spray of B12, or better yet, asking their doctor to try a series B12 injections. Sometimes folate  (the natural form of another B vitamin, often referred to as "folic acid,"  which is a synthetic form not properly assimilated by many people), should also be taken to accompany the B12 for the very best results.