Magnesium supplements have been linked with easing feelings of anxiety, improved sleep and recovery, and reducing the severity of PMS cramps. But magnesium isn’t all fun and relaxation, as 33-year-old Olivia Williams has been finding out. She started taking 500mg capsules of magnesium oxide to help with her anxiety and soon discovered an unwanted side effect.

“I started taking magnesium at the start of the year, and it did wonders for my mental health and general mood,” says Williams. “However, it seemed to make my period late. My cycle has always been very regular, so when I realised that I was four days late, I panicked about potentially being pregnant. I started googling, and I found so many Reddit threads by women who’ve been taking magnesium and have experienced the same thing. 

“I stopped taking the supplement and my period arrived a few days later – a week later than normal. It’s such a shame, as my anxious feelings have now returned.”

It may seem a little far-fetched to suggest that magnesium was entirely to blame; we know that our menstrual cycles can be vulnerable to stress, changes in mood, exercise and even travelling. But following Williams’s advice, we took a deep dive on Reddit and numerous women posting about magnesium disrupting the start of their cycle. Redditors reported a period delay of anything from a few days to a whole month – the majority of whom found that their cycles soon returned to normal once they stopped taking the mineral.

Williams tried looking for research to explain what was happening, but as yet, there are zero clinical studies on the effects of magnesium on cycle length. Stumped, we decided to put our detective hats on.

The NHS states that the RDA for magnesium for women aged 19-64 is 270mg. However, supplements often contain a much higher dose than this. Taking more than 400mg of magnesium a day for a short time can cause diarrhoea, but the NHS admits that “there’s not enough evidence to say what the effects might be of taking high doses of magnesium for a long time”.

Researchers have already confirmed that nutritional deficiencies can lead to menstrual irregularities, but what about the opposite? Could too much of a nutrient also disrupt the cycle?

Magnesium aids in the production of progesterone, and research shows that a lack of progesterone can lead to luteal phase deficiency. This is when the time from ovulation to menstruation lasts for less than nine days (it’s 12–14 days in most people). If too little magnesium can bring about an early period, is it possible that too much magnesium can cause a late period? We put the question to Dr Mohammed Enayat, GP and founder of HUM2N, a next-generation longevity clinic in London.

“In short, yes,” suggests Dr Enayat. “Progesterone is the dominant hormone in the luteal phase; by aiding progesterone synthesis and receptors, magnesium can help sustain the luteal phase.

“Magnesium can also curb prostaglandins and inflammation that trigger menstruation. Higher magnesium levels help regulate prostaglandins and inflammatory cytokines that would otherwise signal the shedding phase. This may delay the dropping progesterone needed for menses.”

Another theory is that magnesium could indirectly affect cycle length by influencing how other nutrients work.

“Excessive intake of any supplement, including magnesium, can disrupt the balance of other nutrients, some of which are also important for menstrual health,” explains Adeem Azhar, clinical pharmacist and co-founder of Core Prescribing Solutions. “For instance, high levels of magnesium can affect the absorption and balance of calcium, vitamin D and other minerals, potentially impacting hormonal health and menstrual regularity.”

It’s natural to freak out about a late period, but in people with magnesium deficiency (it’s thought that 15-30% of us are deficient), a slightly longer luteal phase after taking magnesium supplements could be a sign that your cycle is correcting itself. This is especially important if you’re trying to get pregnant.

“Magnesium helps modulate stress hormones that can reduce luteinising and follicle stimulating hormones, resulting in a defective luteal phase,” explains Dr Enayat, “so supplementing with magnesium has the ability to increase luteal phase length and correct shortened luteal phases associated with deficiency. This helps support better fertility and pregnancy outcomes.”

Research shows that taking a higher-than-recommended intake of magnesium, vitamin A, vitamin C, iron and total folate is linked to a reduced risk of female infertility. Magnesium supplementation has also been shown to reduce the chance of pregnancy complications. That, of course, doesn’t mean that you should intentionally look to take more of a magnesium supplement than is advised on the bottle or packet, and it’s always a good idea to check in with your GP before starting a new vitamin regime – especially if you’re pregnant.

Before anything else, it’s important to make sure that nothing else might be to blame for a delayed period. Do a pregnancy test, assess your stress levels and recent dietary or exercise tweaks. Make a note of any other symptoms that might be linked and take them to a medical appointment if your period doesn’t turn up.

If you do really think that magnesium is to blame, try a smaller dose rather than attempting to cut it out of your regime completely. “Gradually reduce your magnesium supplement dosage rather than stopping abruptly; this allows your body to adapt more smoothly,” says Dr Enayat.

“Go with a low therapeutic dose rather than mega-dosing, and monitor your cycle after dose changes to assess impact. It may take one to two cycles for menstrual rhythm to regulate after down-titrating your magnesium intake.

“Look for magnesium forms that may be better tolerated, such as magnesium glycinate or magnesium taurate, if magnesium dosage itself is proving tricky.”

If you’re looking to up your magnesium intake but find that you’re not tolerating supplements, you can always try the natural route.

“The best way to get your magnesium fix is through whole foods like leafy greens, beans, nuts and whole grains,” says Dr Naheed Ali, a physician and nutritionist. “However, it’s smart to loop in your healthcare provider to help you see the bigger picture. If they think you would benefit from a supplement, they can help you figure out just the right amount for you.”

Of course, without sufficient clinical research, we can only hypothesise about some of the potential effects of magnesium on cycle length. There are many factors at play when it comes to our bodies, so if you’re concerned about any aspect of your menstrual health, it’s always best to speak to your GP.

Images: Getty