Scientists Find Taking Magnesium Alongside Vitamin D Has Surprising Side Effect

For the study, researchers split nearly 240 people into two groups. One group was given a magnesium supplement that was tailored to their usual diet; Another took a placebo. (The average dosage of magnesium was around 200 milligrams.)

The researchers discovered that magnesium, which is important for vitamin D absorption in the body, didn’t universally raise vitamin D levels. Instead, it lowered vitamin D levels in people whose levels were already high and increased them in those who were low.

If you take vitamin D, it’s understandable to wonder if adding a magnesium supplement is the best way to get the most out of your vitamin D absorption. Here’s what experts want you to keep in mind.

What does magnesium do?

Magnesium is a mineral in the body that’s naturally present in many foods, per the National Institutes of Health (NIH). Magnesium is a cofactor (meaning, it’s needed to create a reaction) in more than 300 enzyme systems in your body. That means it plays a role in protein synthesis, blood sugar management, and blood pressure regulation, energy production, the development of bone, and more, according to the NIH. Basically, it does a lot.

The recommended daily intake (RDI) of magnesium varies, but it’s suggested that adult men aim to have 400 to 420 milligrams a day, while adult women should strive for 310 to 400 milligrams of magnesium a day.

What does vitamin D do?

Vitamin D is a fat-soluble vitamin that’s naturally present in some foods and added to others, according to the NIH. Your body can also make vitamin D from vitamin D synthesis, which happens when UV rays from the sun hit your skin. Vitamin D is linked to mental health, calcium absorption, and immune health, among other things, per the NIH.

It’s recommended that most adult women and men try to get 15 micrograms or 600 IU of vitamin D a day.

Why might magnesium regulate vitamin D?

There are likely a few things happening here. One is that magnesium is required for the body to absorb vitamin D, says Scott Keatley, R.D., a nutritionist and co-owner of Keatley Medical Nutrition Therapy.

“Magnesium is required for the enzymes that convert vitamin D into its active and circulating forms, so low magnesium can impair that process,” he explains.
“Correcting a deficiency may help raise vitamin D levels in people who are low by improving activation and transport.”

Qi Dai, M.D., Ph.D., lead study author and a professor of medicine at Vanderbilt University Medical Center, says his work suggests that magnesium regulates the body’s circulating vitamin D levels by regulating its vitamin D synthesis (again, how the body creates vitamin D from sunlight) and metabolism enzymes. But it also seems to tweak vitamin D levels in the gut through specific gut microorganisms, Dai says. That requires someone to have proper functioning of TRPM7, he adds.

“Simply put, magnesium helps your body utilize vitamin D efficiently, both in the gut and throughout the body,” says Keri Gans, R.D.N., author of The Small Change Diet.

Gans stresses that being low in vitamin D isn’t just about one nutrient. “Magnesium, along with diet and lifestyle, may be important,” she says. “Nutrients work together, so taking a balanced approach is essential.”

Should you take a magnesium supplement if you’re low in vitamin D?

Not necessarily. “If someone is low in vitamin D, supplementation with vitamin D remains the primary intervention,” Keatley says. It’s also a good idea to get sun exposure and eat foods that are rich in vitamin D, Dr. Dai says.

At the same time, “it is important to consider consuming foods rich in magnesium or magnesium supplementation, as magnesium can both increase vitamin D levels when it is low and reduce the levels when it is too high,” Dr. Dai adds.

Magnesium is “widely available in a lot of different foods, but they tend to be foods a lot of people don’t eat enough of in the standard American diet,” says Jessica Cording, R.D., a nutritionist and the author of The Little Book of Game-Changers. “In that case, I have seen a supplement be helpful,” she says.

Making sure you get enough magnesium in your diet may help your body respond more effectively to vitamin D, especially if you’re not getting enough of it from the sun or your diet, Keatley says.

But dietitians stress that you shouldn’t just put yourself on a magnesium supplement without checking in with a healthcare provider. “Just because it’s a supplement doesn’t mean it’s without risk,” Cording says.

Magnesium has potential drug interactions with certain medications, including oral bisphosphonates, some antibiotics like doxycycline and ciprofloxacin, diuretics, and proton pump inhibitors. So, it’s important to talk to a healthcare provider if you’re interested in a magnesium supplement.

Other ways to get magnesium in your diet

Keatley recommends starting with food. That means focusing on these magnesium-rich options:

• Pumpkin seeds, 156 mg per ounce
• Almonds, 80 mg per ounce
• Spinach, 78 mg per ½ cup
• Black beans, 60 mg per ½ cup
• Salmon, 26 mg per 3 ounces

“These foods provide fiber and other nutrients beyond magnesium,” Keatley says.

But if you’re concerned that you may be low in vitamin D or magnesium, experts stress the importance of talking to a healthcare provider. They can give you a blood test to check your nutrient status, and make recommendations from there, Cording says.

“If intake is low or there are risk factors for deficiency, a supplement can be considered with clinician guidance,” Keatley says. In terms of magnesium, “forms like magnesium glycinate or citrate are typically better absorbed and tolerated,” he says.

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.