The "sunshine vitamin" aka vitamin D is well known for its immune boosting and bone building effects.
Vitamin D is a mighty important nutrient, yet so many of us are walking around with insufficient levels roaming around in our bodies.
Deficiency can go unnoticed in many individuals as symptoms are often subtle. However, when this becomes a chronic condition it can lead to many health issues such as hypocalcemia, hyperparathyroidism, osteoporosis and symptoms like irritability, lethargy, developmental delay, bone changes, or fractures (1).
Vitamin D deficiency is not an uncommon occurrence, in fact its highly prevalent especially among populations in the Northern Hemisphere, yes we're looking at you Canada!
Vitamin D insufficiency affects up to 40% of adults in the United States and 70% - 97% of adults in Canada (2)(3).
Vitamin D deficiency is a global public health issue that is quickly becoming a widespread problem. It is prevalent in both developed and developing countries, impacting up to 1 billion people around the world (4).
There are many factors that are associated with low vitamin D worldwide including poor dietary intake, malabsorption conditions, lack of sun exposure, and the use of certain medications (5).
Due to the high prevalence of vitamin D deficiency, many people are recommended vitamin D supplements in order to maintain healthy levels of this vitamin.
It is no secret that vitamin D is essential for health, however vitamin D doesn't work solo. It gets by with a little help from its friends, like vitamin K.
How do vitamin D and vitamin K work together?
Animal and human studies suggest that there is a synergistic interplay between vitamin D and K (6).
How do they work together you may be wondering?
Well, these fat soluble vitamins work together in a number of ways.
Vitamin D stimulates the production of certain proteins that transport calcium, and these proteins depend on vitamin K to be activated.
Vitamin K specifically activates osteocalcin, one of the main proteins found in bone. Osteocalcin is responsible for binding calcium to the bone, supporting bone strength and flexibility.
Vitamin D and K2 work together to strengthen bones and support the health of the heart and arteries.
While vitamin D increases the absorption of calcium in the body, vitamin K shuttles this calcium from the bloodstream to our bones. High amounts of vitamin D without vitamin K can cause calcium to accumulate in the blood vessels, which is a risk factor for heart issues.
When we have enough vitamin K with vitamin D, this can help to reduce calcification in the vessels by depositing calcium in the right places in the body, such as the bones and teeth. This means that vitamin K can help to prevent negative effects of excess vitamin D.
A meta analysis found that the combination of vitamin K and D can significantly increase total bone mineral density (8).
Combining vitamin D with vitamin K may be more beneficial than supplementing these vitamins on their own, and more particularly for bone and heart health (9).
Is it harmful to supplement vitamin D without vitamin K?
Vitamin D supplements are generally considered very safe, and toxicity is uncommon (10). Problems are most often associated with extremely high doses of vitamin D supplementation which can result in health consequences such as hypercalcemia, or elevated serum calcium levels (11)(12).
Vitamin K may help to prevent this from happening.
A higher intake of vitamin D from supplementation may represent a higher risk for cardiovascular issues, particularly in people who are deficient in vitamin K.
Not only have high levels of vitamin D been linked to hypercalcemia, a risk factor for heart disease, low levels of vitamin K have been linked to an increased risk of blood vessel calcification (13)(14).
Higher dietary intake of vitamin K has been associated with a decreased risk of coronary heart disease and research suggests that it may play an important role in the prevention of cardiovascular disease (15)(16).
Though research indicates that supplementing high levels of vitamin D without vitamin K may be a concern, more evidence is needed to reach a definite conclusion.
If you are supplementing with higher doses of vitamin D, we always recommend following expert advice and monitoring your levels with your doctor.
In addition, if you are taking vitamin D over the long term, vitamin K may be worthwhile investigating as an additional supplement or as a combined formula.