Evidence summary
What it does: Involved in hundreds of enzymatic reactions; appears to reduce testosterone binding to SHBG.
Studied dose: 10mg per kg body weight in the main trial; 200 to 400mg elemental is typical supplementally.
Evidence quality: Limited but coherent.
Key requirement: A well-absorbed form.
The evidence
The most cited trial examined magnesium supplementation at 10mg per kilogram of body weight for four weeks in sedentary men and in tae kwon do athletes. Both free and total testosterone increased, with the largest increases in the exercising group.1
Mechanistically, magnesium appears to reduce the binding affinity of testosterone for SHBG, increasing the free fraction, which is the same lever boron operates on. In vitro work supports this interaction.2
The evidence base is small. What makes magnesium worth including is less the strength of the hormonal data and more the prevalence of inadequate intake in Western diets.
The form determines the dose you actually get
This is the practical point, and it is where most products quietly fail.
Magnesium cannot be sold in elemental form; it must be bound to a carrier, and that carrier determines both the elemental content and how much is absorbed:
| Form | Absorption | Notes |
|---|---|---|
| Oxide | Poor | Cheapest, high elemental content on paper, largely unabsorbed. Better known as a laxative. |
| Citrate | Good | Well studied, good all-round choice. |
| Bisglycinate | Good | Gentle on the stomach, bulky, so real doses need larger capsules. |
| Malate | Good | Less studied than citrate. |
A label stating "Magnesium 400mg" without naming a form is providing incomplete information. Worse, a label stating "Magnesium bisglycinate 2,000mg" is describing the whole compound; the elemental magnesium inside is roughly 200mg. The honest format is "Magnesium (as bisglycinate) 200mg".
Dosing
The RDA for adult men is 400 to 420mg daily from all sources including food. Supplemental doses of 200 to 400mg elemental are typical. Split doses absorb better than a single large one, and evening dosing suits magnesium well given its effect on sleep quality.
Bottom line
Magnesium is worth correcting because shortfall is common, and the form on the label tells you whether a manufacturer was optimising for cost or for absorption. It is a reliable signal of formulation care, which is why it features in our scoring.
References
- Cinar V, Polat Y, Baltaci AK, Mogulkoc R. Effects of magnesium supplementation on testosterone levels of athletes and sedentary subjects at rest and after exhaustion. Biological Trace Element Research. 2011;140(1):18-23.
- Excoffon L, Guillaume YC, Woronoff-Lemsi MC, Andre C. Magnesium effect on testosterone-SHBG association studied by a novel molecular chromatography approach. Journal of Pharmaceutical and Biomedical Analysis. 2009;49(2):175-180.