"Cause" is the literal opposite of "consequence", unless you're postulating a feedback loop.

Depends how you read the line.

If you read it this way, they are the same.

> "High blood pressure may be not [be] a cause of cognitive decline, but [cognitive decline may] just [be] a consequence [of high blood pressure]."

The other interpretation makes less sense.

> "High blood pressure may be not a cause of cognitive decline, but just a consequence [of cognitive decline]."

The implication here is that cognitive decline causes high blood pressure, which doesn't make any sense.

The author I think was trying to say they have a common cause, but I don't believe there's any evidence for the mechanism on which their thesis relies.

The implication is that a dying brain (= cognitive decline) initiates a flight or fight response which includes adrenaline flare ups and high blood pressure as a result.

A consequence of cognitive decline.

You're right that it can be read both ways.