Does a magnesium deficiency make you more sensitive to stress?
A low magnesium level is associated with greater sensitivity to stress. In some people with mild anxiety, supplements help, though results are inconsistent.
A low magnesium level is associated with greater feelings of anxiety and stress. That link has been reported repeatedly, but the evidence is weak: no study has shown that a magnesium deficiency is the cause. The relationship may also run in the opposite direction, because stress itself depletes magnesium.
Magnesium supplements reduce anxiety in some studies, but far from all. In people who were already prone to anxiety, roughly half of the studies examined found a positive effect. For mild anxiety that was four out of eight studies, and for premenstrual complaints four out of seven. In women with painful periods, magnesium alone had no measurable effect on stress.
The combination of magnesium with vitamin B6 did show a clear effect on premenstrual anxiety, whereas magnesium as a single supplement had no effect in that same context. That is a striking difference that the studies do not explain further.
For anxiety and stress, magnesium falls into the category of goals for which people buy it but for which evidence is lacking. The quality of the evidence is too low and the results too inconsistent for a targeted recommendation. If you are curious whether magnesium does anything for your stress levels, there is no solid basis for trying it specifically for that purpose.
This answer draws on two summaries of available studies on magnesium and anxiety/stress in people. The researchers themselves rate the quality of the evidence as low: most of the underlying studies are small, methodologically limited and not well controlled. There are no well-designed studies in people that causally confirm the link between magnesium deficiency and stress. For supplementation, the results are inconsistent and partly contradictory, which further limits the strength of the evidence.