LONDON, July 2 -- For decades, the cardiovascular math of obesity was unforgiving. Higher body weight meant higher blood pressure, higher cholesterol, and a measurably shorter life. That relationship was taught in medical schools as settled biology and broadcast in public health campaigns as an obvious truth. A major new study published Wednesday in The Lancet suggests the math is, quietly and at population scale, beginning to change.

Researchers tracking nearly one million people across seven countries found that middle-aged and older adults with obesity now show blood pressure and cholesterol profiles nearly identical to normal-weight peers of the same age. The mechanism is not that obesity has become harmless. It is that the pharmacol...