A massive study of electronic health data of thousands of British patients spanning decades indicates that blood pressure begins an inexorable decline in the final 14 to 18 years before death.

The declines were general across the population – but were most pronounced in people who had dementia, heart failure, or significant weight loss toward the tail end of their lives, write the researchers in the journal JAMA Internal Medicine.

The declines were also found in those without a hypertension diagnosis, or who were on blood pressure medications, they add.

“These blood pressure decreases are not simply attributable to age, treatment of hypertension, or better survival without hypertension,” they conclude. “Late-life blood press decreases may have implications for risk estimation, treatment monitoring, and trial design.”

The study looked at the Clinical Practice Research Datalink primary care information in the United Kingdom.

The group of 46,634 were 60 or over, and died between 2010 and 2014. All the patients had detailed blood pressure records spanning years.

The blood pressure rates peaked between 14 and 18 years before the deaths – and then decreased progressively. The decrease was linear from 10 to three years before death – but accelerated in the last two years of life, they report.

But the underlying reason for the across-the-board pressure decreases still needs to be understood.

“Observational studies such as ours need to be followed by rigorous clinical trials in order to guide clinical care guidelines,” said George Kuchel, one of the authors, and director of the University of Connecticut Center on Aging.

The new study comes on the heels of new guidelines by the American Heart Association. Those guidelines, released last month, would reclassify half of all Americans as having high blood pressure.