Many older patients in the U.S. are taking drugs to thin  their blood and prevent abnormal blood clotting.
  The most commonly used one is Coumadin, also known as  warfarin. This drug works by interfering with vitamin K. It works because  vitamin K is critical for blood clotting. So when you take vitamin K out of the  picture, the blood can’t clot.
  But like most vitamins, vitamin K has many other functions  in the body besides blood clotting. One of those functions is brain physiology  and function.
  So recently, scientists wondered if taking an anti-vitamin K  blood thinner increases the chance of developing dementia.
Researchers examined 267 men and women between the ages of  75 and 91. Some of them were taking an anti-vitamin K blood thinner and some  weren’t.
  They gave each of the men and women a Mini-Mental State  Examination (MMSE). The MMSE is a simple cognitive function test that a doctor  can do in the office in less than 15 minutes. A perfect score is 30. A score  less than 25 indicates cognitive impairment.
  Then they compared the scores of the men and women on the  anti-vitamin K drugs vs. the ones who weren’t. When they made the comparison,  they also took into account any factors that might influence the results, such  as age, sex, weight, health status, and mood. Here’s what they found.
Out of the total 267 men and women, 197 scored  less than 25 on the MMSE test. And the risk of being in
that group was 17.4% higher in those who were taking an  anti-vitamin K drug.
  Another study reported just a couple of years ago in the Journal  of Neurobiological Aging also looked at brain performance and vitamin K  levels. Researchers looked at 320 men and women aged 70 to 85 years who had no  obvious signs of any cognitive impairment.
  Then they checked their memory, brain speed, and their  vitamin K blood levels. The researchers found that the higher the vitamin K  levels were, the better their verbal episodic memory and brain speed.
  Your episodic memory is important for everyday life. For  example, remembering where you put your keys is an example of episodic memory.
  The authors of the study concluded: “Our study adds evidence  to the possible role of vitamin K in cognition during aging, specifically in  the consolidation of the memory trace.” How can vitamin K be so important for  brain function? Two ways for sure.
  For one, vitamin K is involved with the metabolism and  regulation of sphingolipid metabolism. Sphingolipids are fats that are a major  component of brain cell membranes that have a significant role in the structure  and function of the nervous system. They are biologically potent molecules that  are involved in a wide range of brain-cell actions.
  Also, there’s growing evidence that vitamin K has  anti-inflammatory activity and protects the nervous system from free radical  damage.
  So if your doctor has you taking a drug like Coumadin that  interferes with vitamin K, perhaps you should look into an alternative.
  Although there are no published studies to prove it, I  believe that the combination of nattokinase, fish oil supplements, and 81 mg of  aspirin is a safe and excellent way to do this.
  Many doctors, including myself, have been using this  combination for decades and have never seen a bad result.
Source:
Annweiler, C., G. Ferland, et al. “Vitamin K antagonists and  cognitive impairment: results from a cross-sectional pilot study among  geriatric patients.” J Gerontol A Biol Sci Med Sci. 2015 January;70(1):97-101.
Presse, N., S. Belleville, et al. “Vitamin K  status and cognitive function in healthy older adults.” 
Neurobiol