Although people often supplement with vitamin D, they don't realise that magnesium is just as important. It optimises levels in those who are deficient and lowers it in the very few of us who have high levels, say researchers from Vanderbilt University Medical Center.
Vitamin D is vital for our wellbeing, yet several studies have recently suggested it raises the risk of colorectal cancer. Looking at the evidence again, the Vanderbilt researchers say the real problem is that the people studied were low in magnesium, and vitamin D is dangerous only when it's not regulated.
When levels are neither too high or low, it protects against heart disease, cancers and many other health issues, the researchers have found. And that can be achieved only when magnesium levels are also high enough.
The theory was tested on 250 people, at risk of developing colorectal cancer, who were given either magnesium or a placebo supplement.
The researchers reckon that up to 80 per cent of people are deficient in magnesium. As well as supplements, magnesium is also in dark green leafy greens, beans, whole grains, dark chocolate, fatty fish, nuts and avocado.