When we take supplements, we don’t often think about how they interact with each other. It’s the same with research. Nutrients are typically studied individually to see whether they produce a benefit or not. But our bodies don’t work that way. Nutrients don’t work alone, and there’s an intricate balance between them, known as homeostasis, that keeps the body in balance.
It’s important to understand these relationships, as they can affect health benefits, optimal dosages, and even side effects. In a previous article, we explored the importance of vitamin D and how much we should be taking. The next question is whether, as some suggest, we need to take magnesium and K2 along with it.
Vitamin D Activation
Vitamin D is a fat-soluble vitamin. In order to become active, it goes through various processes in the body. Simplistically, the process starts when the skin is exposed to sunlight, when we eat certain foods (like fatty fish, dairy products, and eggs), or when we take a supplement.
The inactive form of D initially goes to the liver, where it’s converted (hydroxylated) to calcifediol, also known as 25-hydroxycholecalciferol (25(OH)D). It’s then transformed in the kidneys into a biologically active form: 1,25-dihydroxyvitamin D (1,25(OH)2D). In both of these steps, in the liver and kidneys, magnesium is required.
Once vitamin D leaves the kidneys, it’s transported by carrier proteins. This is also a magnesium-dependent process, and a lack of adequate magnesium may reduce the amount of vitamin D absorbed.
Another concern is that higher doses of D may lead to a buildup of calcium, possibly leading to calcification of the blood vessels, osteoporosis, or kidney stones (1). This is another reason to consider taking a magnesium supplement along with your vitamin D.
Magnesium and vitamin D Work Together
Magnesium is an essential vitamin involved in more than 300 metabolic functions, with 90% of total body magnesium being contained in the muscles and bones. It has many vital functions, playing a role in bone health, energy production, muscle contraction, conduction of nerve impulses, maintaining blood pressure, and even heart rhythm.
Magnesium is found in a variety of foods such as almonds, bananas, green vegetables, beans, salmon and other fatty fish, milk, eggs, mushrooms, flaxseeds, pumpkin seeds, whole grains, and dark chocolate. Yet according to Costello et al, 2016 (2), approximately 48% of the US population are not getting enough magnesium from food.
This is in large part due to the increasing reliance on high amounts of processed foods, refined carbohydrates, and added sugars along with fewer fruits, legumes, and vegetables in the daily diet. Farming practices and poor soil quality may be further contributing to this high deficiency rate.
Magnesium deficiency and what to do
Kidney disease, gastrointestinal disorders, some cancers, medications (including diuretics, insulin, and proton pump inhibitors), stress, and strenuous exercise can also lead to magnesium deficiency (3).
If there’s too much or too little magnesium, the kidneys will try to bring levels back into balance. When levels are too low for the kidneys to compensate, magnesium is primarily drawn from the bones as well as from the muscles and other internal organs (4).
Increasing vitamin D intake increases our magnesium requirements. When magnesium levels are already depleted, this can lead to further loss. This weakens D’s ability to perform its many functions – one of which is to help increase the absorption of magnesium in the intestinal tract to maintain magnesium balance.
Does this mean you must always take magnesium with vitamin D?
Some would argue that if you’re eating a balanced diet and your magnesium levels are good, you may not need to supplement with magnesium when taking vitamin D.
In a large study by Deng et al, (2013), the researchers looked at magnesium, vitamin D status, and the risk of mortality. Their results showed that a high intake of total magnesium (either from food or supplements) was “independently associated with significantly reduced risks of vitamin D deficiency and insufficiency respectively” and “the associations between serum 25(OH)D and risk of mortality may be modified by the intake level of magnesium” (5).
This suggests that if you’re taking high doses of vitamin D and you’re sure of your magnesium status, it’s probably a good idea to take a supplement.
The Health Benefits of Vitamin K2
Vitamin K is another fat-soluble vitamin, but it’s not a single vitamin. There are two forms of vitamin K, K1 and K2, which act somewhat differently in the body.
K1 (phylloquinone) is found in leafy green vegetables and some vegetable oils. It regulates coagulation factors that are involved in helping the blood to clot.
K2 (menaquinone) can be found in foods such as butter, egg yolks, natto, some cheeses, and fermented dairy products. It’s also produced in small quantities by lactic acid bacteria in the intestines. There are different forms of K2 as well. The MK-7 form has been found to have greater bioavailability than other forms (such as MK-4) and is therefore regarded as the best for supplementation.
Keeps Bones Healthy
K2 activates inactive proteins such as osteocalcin (bone Gla protein), which helps to keep bones healthy, and matrix Gla protein (MGP), which helps to reduce calcium deposits in the arterial wall (6). By activating these proteins, K2 helps to direct calcium to the bones rather than the blood vessels.
Vitamin K stores are limited in the body, and whilst the body can recycle vitamin K to some extent, there’s a growing concern that our dietary intake and other factors (such as the use of antibiotics and anti-coagulant drugs) are detrimentally affecting vitamin K levels.
Why is vitamin K important when taking vitamin D?
Scientists have proposed that higher doses of vitamin D may lead to the increased production of vitamin K-dependent proteins (osteocalcin and matrix Gla protein) and that if there is insufficient vitamin K, these proteins will remain inactivated. This could lead to lower bone mineral density and increased risk for calcification of the arteries (and therefore an increased risk for cardiovascular disease).
According to Ballegooijen and colleagues (2017), studies have shown some evidence of improved bone mineral density when taking both vitamin D and K, especially in post-menopausal women (6).
There have been few studies on humans looking at the combined effects of vitamin D and K when it comes to cardiovascular health. However, the results suggest that there may be some benefit when taking vitamin D and vitamin K2 (MK-7) in combination (6).
Another risk of increasing vitamin D intake along with a calcium supplement is the effect this combination has on intestinal calcium absorption. If vitamin K levels are low, according to Ballegooijen and colleagues (2017), this may lead to excess calcium being deposited in the blood vessels rather than in bone (6).
A Word of Caution
When supplementing with vitamins D and K, the literature suggests taking K2 (MK-7) rather than K1, which is involved in blood coagulation. If you’re taking anticoagulants (warfarin is a common one), you should avoid K1 – and even K2 isn’t recommended without the approval of a medical professional (7).
So where does that leave us?
We often get caught up in thinking we’ll get these super-duper health benefits when we up our dosage of a supplement. As we see in the case of vitamin D, it’s a little more complicated than we thought. On top of that, there’s a shortage of human studies.
If you’re eating a balanced diet with sufficient magnesium and vitamin K2, you may not need to take additional supplements with vitamin D. But things change when you throw additional calcium into the mix, and K2 may be required.
If you’re not eating a balanced diet, it’s best to check your levels of magnesium, K2, and calcium before taking high doses of vitamin D over the long term.