Blood pressure barely moved on average, more at 400mg a day
Averaged over 8,610 people, magnesium lowered the upper reading by 1.25 points. In the slice taking 400mg a day or more for at least 12 weeks it was 6.38, a figure found by looking back.
What the study found
Magnesium moved blood pressure a point on average, six at 400mg a day
That larger number belongs to a slice of the data: 400mg of magnesium a day or more for at least 12 weeks, where the drop was 6.38 points on the upper blood-pressure reading. Averaged over all 8,610 people it was 1.25. A separate pooling of 34 trials put the threshold near 300mg a day.
The caveat · Bigger drop found after the fact
The larger figures come from a slice of the data examined after the fact rather than the review's main comparison, which makes them the weaker number even though they are the more striking one. The ten pooled reviews overlap, so some of the same original trials are counted more than once. And blood pressure is a stand-in here: none of these trials counted heart attacks or strokes.