The Short Answer

Vitamin D supplementation works best when paired with specific co-factors, vitamin A, magnesium, and K2, that help your body absorb and use it properly. Most people are deficient in vitamin D, and this deficiency is especially problematic for those with autoimmune conditions because adequate levels help reduce inflammation. Testing your vitamin D regularly ensures you maintain optimal levels without oversupplying.

Why Vitamin D Co-Factors Matter for Autoimmune Health

Sufficient vitamin D levels require both a healthy diet and adequate sunlight exposure, yet modern life has made it difficult to obtain both. About half the world’s population and three-quarters of the US population are deficient in vitamin D, even in sunny locales. Sufficient vitamin D is vital to dampening inflammation and supporting immune regulation in autoimmune diseases. For example, people managing Hashimoto’s low thyroid often see improvements in symptoms when vitamin D levels normalize. Some individuals with autoimmunity may even need extra vitamin D due to a genetic variation that affects how their cells absorb it.

When supplementing with vitamin D (cholecalciferol), discussion would not be complete without highlighting its cofactors — “helper molecules” that assist in biochemical transformations and improve bioavailability.

Building Your Vitamin D Support System: The Essential Co-Factors

When supplementing vitamin D, make sure to include fat-soluble vitamin A, magnesium, and K2, as they make it more bioavailable and help prevent D overload.

Vitamin A and vitamin D work together to ensure your genetic code plays out properly. There are two main types of vitamin A:

• Beta-carotene, found in brightly colored fruits and vegetables, such as apricots, mango, and leafy greens
• Retinol, found in organ meats and dairy products

While vitamin A can be taken as a supplement in the form of beta-carotene or retinol, it’s possible to take too much retinol. Your body can’t easily eliminate excess retinol, which can be harmful. However, your body can dispose of excess beta-carotene more readily.

Magnesium is abundant in food, but high doses of vitamin D3 deplete the body of it. If you are already low in magnesium and taking vitamin D, supplementation becomes important to avoid headaches, cramping, nausea, numbness, and other symptoms that may emerge when beginning high-dose D3.

The Vitamin D Council recommends 500-700mg of magnesium per day. Common supplement sources include magnesium glycinate, magnesium citrate, and magnesium malate. Each has unique effects, so consult a functional medicine doctor to find the one that’s right for you.

Foods rich in magnesium include dark leafy greens, potatoes, beans, lentils, avocado, bananas, figs, strawberries, blackberries, nuts, seeds, brown rice, and dark chocolate.

Vitamin K2 prevents a serious side effect of vitamin D overload: soft tissue calcification. When vitamin D is high but not toxic, some studies show it may even protect against calcium deposits in arteries.

Vitamin K2 is a critical cofactor for vitamin D because it helps your body deposit calcium in appropriate locations, bones and teeth, while preventing calcium from accumulating where it doesn’t belong, such as soft tissues, arterial walls, joints, and organs.

Vitamin K2 comes partly from gut flora conversion of vitamin K1 from dietary sources such as cabbage, kale, spinach, chard, green leafy vegetables, broccoli, cauliflower, Brussels sprouts, and sauerkraut.

The National Academy of Sciences recommends a daily intake of 90 mcg for women and 120 mcg for men. The journal Osteoporosis International recommends an optimal dose of K2 (as MK-7) of 180 mcg/day.

Caution: If you take blood-thinning medications such as Warfarin or Coumadin, avoid vitamin K supplements, as they can affect how well your blood clots.

Testing Your Vitamin D Levels: What Optimal Actually Means

Having your vitamin D level checked periodically can improve your overall health outcomes, particularly if you’re managing an autoimmune condition. In functional medicine, vitamin D levels are measured with a serum 25-hydroxy vitamin D test. Optimal levels are considered to be between 50 and 80 ng/mL, depending on the individual. Levels above 100 ng/mL may indicate vitamin D overload and risk of artery calcification.

If you have leaky gut or are managing autoimmune conditions like Hashimoto’s low thyroid, you may be more prone to recurring vitamin D deficiency. Testing your levels initially and then rechecking periodically ensures you maintain adequate status over time without accumulating excess.

Contact RedRiver Health and Wellness to work with a functional medicine doctor who can help optimize your vitamin D and cofactor levels for your specific autoimmune condition.