Vitamins D3 and K2 play vital roles in supporting whole-body wellness, yet many people don’t realize just how essential they are until symptoms of deficiency begin to appear. These two fat-soluble vitamins work behind the scenes to help maintain strong bones, support immune function, and promote cardiovascular and mood health. But what happens when your levels fall short?
Deficiencies in either vitamin can lead to a range of health concerns—some subtle, others more serious. Without enough vitamin D, for example, your body may struggle to absorb calcium efficiently, potentially impacting bone strength, as well as affecting immune resilience, and even mood balance. Meanwhile, vitamin K is a key player in both healthy blood clotting and the regulation of calcium in the body—helping to keep it in bones and out of arteries, where it doesn’t belong.
Unfortunately, deficiencies in these nutrients are more common than many realize. According to data from the National Health and Nutrition Examination Survey (NHANES), approximately 41% of U.S. adults are deficient or insufficient in vitamin D when measured against the FDA’s Recommended Daily Intake (RDI). But if we consider the Optimal Daily Intake (ODI)—levels that many integrative health experts believe better support long-term wellness—that number could climb much higher. Vitamin K deficiency is less frequently discussed, but still significant. While overt deficiency is less common, many Americans may not be meeting optimal vitamin K intake, especially vitamin K2, which is not as abundant in the standard Western diet.
In this article, we’ll explore how vitamins D and K function in the body, common causes of deficiency, and how to recognize the symptoms. You’ll also learn who is most at risk, how to test your levels, and the most effective ways to restore and maintain healthy vitamin D and K status—including nutrition, lifestyle strategies, and targeted supplementation.
The Role of Vitamin D in the Body
Often referred to as the “sunshine vitamin,” vitamin D is much more than just a seasonal nutrient. It plays a critical role in a wide range of biological functions that keep your body strong, resilient, and balanced.
One of vitamin D’s most important jobs is supporting calcium absorption, which is essential for maintaining healthy bones and teeth. Without adequate vitamin D, your body may absorb only a fraction of the calcium you consume—even if your diet is rich in dairy or leafy greens. Over time, this can weaken the skeletal system and contribute to bone loss.
But bone health is just one piece of the puzzle. Vitamin D also plays a key role in immune system modulation. It supports the production and regulation of immune cells that help the body identify and respond to potential threats. Maintaining optimal vitamin D levels has been linked to enhanced immune resilience and a lower risk of certain seasonal challenges.
In addition to physical health, vitamin D also impacts mental well-being. It supports the production of neurotransmitters like serotonin—often referred to as the “feel-good hormone”—which plays a role in mood regulation. This may help explain why lower vitamin D levels are commonly observed in individuals experiencing mood imbalances, particularly during the darker, colder months of the year.
Another key function of vitamin D is its ability to help maintain a healthy inflammatory response. By influencing how certain genes and cells behave, vitamin D helps the body manage normal inflammation, a foundational element of long-term wellness.
Despite its importance, vitamin D is unique in that it’s not widely available in food. Instead, the primary source is sunlight—specifically, UVB rays that help the skin synthesize vitamin D3. However, factors such as sunscreen use, limited outdoor time, age, skin tone, and geographic location can all limit natural production, making deficiency more likely than many people realize.
The Role of Vitamin K in the Body
While often overshadowed by more well-known nutrients, vitamin K plays a critical role in maintaining foundational aspects of health—particularly in blood clotting and bone strength. It’s a fat-soluble vitamin, meaning it’s absorbed best with dietary fats, and it comes in several forms, each with unique functions and benefits.
The most recognized form, vitamin K1 (phylloquinone), is primarily found in green leafy vegetables and plays a key role in blood coagulation—helping your body form clots when needed to prevent excessive bleeding. This is essential for healing wounds and maintaining overall circulatory stability.
Then there’s vitamin K2 (menaquinone), which is less abundant in the average diet but arguably just as important—especially for bone and cardiovascular health. Vitamin K2 helps regulate calcium by activating proteins that guide it into bones and teeth while preventing it from accumulating in soft tissues like arteries. Without adequate K2, calcium may not be efficiently utilized, potentially impacting both skeletal and heart health.
Vitamin K2 comes in multiple subtypes—MK-4 and MK-7 being the most researched. MK-4 is shorter-acting and found in animal products such as eggs, butter, and meat. MK-7, derived from fermented foods like natto, has a longer half-life in the body, making it especially valuable for sustained benefits over time. Ideally, a balanced intake of both forms supports optimal function.
It’s also important to note that not all vitamin K2 is created equal. Some supplements contain a mixture of cis and trans forms of MK-7. The “all-trans” form is nature-identical and bioactive, while the cis form is far less effective. Choosing a supplement with all-trans MK-7 ensures better absorption and efficacy.
Beyond bone and cardiovascular support, emerging research suggests vitamin K2 may also play a role in skin elasticity and brain health, though more studies are needed to confirm these potential benefits.
Because vitamin K2 is scarce in standard Western diets, many people may not be getting enough—especially those with poor gut health, which can interfere with the body’s natural production of K2.
Common Causes of Vitamin D Deficiency
Vitamin D deficiency is surprisingly common—even in sunny regions—and it can occur for several reasons. Despite the nickname “sunshine vitamin,” modern lifestyles and environmental factors often make it difficult to get enough from sun exposure alone.
One of the biggest contributors to low vitamin D levels is a lack of direct sunlight. Vitamin D3 is synthesized in the skin through exposure to UVB rays, but this process is affected by many variables: time of day, season, latitude, age, and skin tone. For example, people living in northern regions of the U.S.—especially during fall and winter—receive little to no UVB exposure for months at a time. Even in sunnier climates, frequent use of sunscreen, indoor living, and protective clothing can block the rays needed to trigger vitamin D synthesis.
Diet is another contributing factor. While some foods like fatty fish, egg yolks, and fortified dairy provide small amounts of vitamin D, few foods naturally contain it, and even fortified foods may not supply sufficient amounts to meet optimal needs—especially when considering the difference between the FDA’s Recommended Daily Intake (RDI) and more robust Optimal Daily Intake (ODI) guidelines supported by emerging research.
Additionally, digestive health and absorption play a key role. Because vitamin D is fat-soluble, individuals with conditions that affect fat absorption—such as celiac disease, Crohn’s disease, or gallbladder dysfunction—may have trouble maintaining adequate levels. Certain medications, including steroids and weight-loss drugs that reduce fat absorption, can also interfere with vitamin D uptake.
Lastly, aging reduces the skin’s ability to produce vitamin D3 efficiently, making older adults more susceptible to deficiency. People with darker skin tones also naturally produce less vitamin D in response to sunlight, putting them at higher risk—particularly in areas with limited sun exposure.
For all these reasons, many individuals may benefit from routine testing and targeted strategies to ensure they’re meeting their vitamin D needs—especially when lifestyle and environment aren’t enough.
Signs and Symptoms of Vitamin D Deficiency
Because vitamin D supports so many vital systems in the body, a deficiency can present in a variety of ways—some subtle, others more pronounced. Over time, low levels can impact energy, mood, bone strength, and immune resilience.
One of the most common early signs of deficiency is fatigue—the kind that lingers even after a good night’s sleep. Since vitamin D plays a role in mitochondrial function and energy metabolism, low levels may contribute to persistent tiredness and a general lack of vitality.
Muscle weakness and aches are also frequently reported. This may be due to vitamin D’s role in muscle cell function and its involvement in regulating calcium, which is essential for normal muscle contraction. In more severe or prolonged deficiencies, individuals may experience bone pain, especially in the lower back, hips, or legs. These symptoms can sometimes be mistaken for arthritis or general aging.
Over time, inadequate vitamin D can lead to bone demineralization, increasing the risk of fractures—particularly in older adults or postmenopausal women. In children, severe deficiency may lead to rickets, a condition marked by soft or deformed bones.
Mental health can also be impacted. Vitamin D supports the production of serotonin and other neurotransmitters, which are involved in regulating mood. Low levels have been associated with seasonal mood changes, feelings of low motivation, and mild mood imbalances—especially during the darker months when sun exposure is limited.
Another red flag? Frequent colds or infections. Vitamin D plays a role in activating immune defenses. When levels are too low, the immune system may become less responsive, leaving the body more vulnerable to common seasonal challenges. Because these symptoms can overlap with other conditions, they’re often overlooked.
Signs and Symptoms of Vitamin K Deficiency
Though often underdiagnosed, vitamin K deficiency can have serious consequences—particularly for bone health, cardiovascular function, and the body’s ability to manage normal blood clotting. Unlike vitamin D, which has gained widespread attention, vitamin K often flies under the radar—yet its role in long-term health is just as essential.
One of the most recognizable symptoms of vitamin K deficiency is easy bruising or excessive bleeding. This happens because vitamin K is required to produce clotting factors—proteins that help stop bleeding when blood vessels are injured. If you bruise frequently, experience nosebleeds, or notice that small cuts take longer to stop bleeding, it may be a sign your vitamin K levels are suboptimal.
Beyond clotting, bone health is also strongly linked to vitamin K status. Vitamin K—especially K2—activates a protein called osteocalcin, which helps bind calcium to the bone matrix. When this process is compromised, bones can lose density over time. This contributes to conditions marked by brittle bones and increased fracture risk. Postmenopausal women and older adults are especially vulnerable.
A lesser-known but increasingly studied symptom of long-term vitamin K deficiency is arterial calcification. When calcium isn’t properly directed into bones, it can accumulate in soft tissues like arteries. This calcification reduces elasticity and may impair normal blood flow. Vitamin K2 activates matrix Gla-protein (MGP), which helps keep calcium out of arterial walls. Without enough K2, this protective mechanism may weaken.
Emerging research also suggests that vitamin K may play a role in skin health and cellular function, potentially influencing elasticity and resilience. However, more clinical data is needed to confirm these additional benefits.
Keep in mind, the early signs of vitamin K deficiency can be subtle. Because K1 is common in leafy greens, many people get enough for clotting, but K2—found in fermented foods and grass-fed animal products—is often lacking in Western diets. That’s why it's important to assess your intake, especially if you experience any of the symptoms mentioned above.
Populations at Higher Risk for Deficiency
While anyone can experience suboptimal levels of vitamins D and K, certain populations are significantly more vulnerable due to lifestyle factors, biological differences, and underlying health conditions.
Older Adults and Postmenopausal Women
Aging naturally reduces the body’s ability to synthesize vitamin D from sunlight. The skin becomes less efficient at converting UVB rays into vitamin D3, and kidney function—which helps convert vitamin D into its active form—can also decline over time. Additionally, postmenopausal women are at higher risk of bone loss due to hormonal changes, making adequate levels of both vitamin D and K2 essential for supporting healthy bone density and reducing fracture risk.
People with Darker Skin Tones
Melanin, the pigment that gives skin its color, can reduce the skin’s ability to produce vitamin D in response to sunlight. As a result, individuals with darker complexions often need significantly more sun exposure to synthesize the same amount of vitamin D as those with lighter skin. When combined with modern indoor lifestyles or northern geographic locations, this can quickly lead to deficiency.
Individuals Living in Northern Latitudes
People who live farther from the equator experience fewer hours of UVB sunlight, especially during fall and winter months. In some areas of the U.S., there is virtually no UVB exposure between October and March, making it nearly impossible to produce vitamin D naturally for half the year.
People with Malabsorption Disorders
Conditions such as celiac disease, Crohn’s disease, ulcerative colitis, and even bariatric surgery can impair the body’s ability to absorb fat-soluble vitamins like D and K. Since both vitamins rely on proper digestion and fat absorption, people with these conditions are at a heightened risk of deficiency—even with a nutrient-rich diet.
Long-Term Medication Use
Certain medications, including antibiotics, cholesterol-lowering drugs, and anticoagulants, may interfere with vitamin K production or absorption. Corticosteroids and some weight-loss drugs can also impact vitamin D metabolism.
Understanding your personal risk factors is key to maintaining optimal levels. Regular testing and targeted nutritional support can make a meaningful difference—especially for those in these higher-risk groups.
How to Test for Vitamin D and K Deficiency
If you suspect you may have low levels of vitamins D or K—or simply want to optimize your wellness—testing can provide valuable insights. Both nutrients play key roles in long-term health, but they require different approaches when it comes to accurate assessment.
Testing for Vitamin D
The most reliable way to measure vitamin D status is through a 25-hydroxyvitamin D blood test (often abbreviated as 25(OH)D). This test reflects the total amount of vitamin D circulating in the body from both dietary intake and sun exposure. While the FDA’s Recommended Daily Intake (RDI) is aimed at preventing deficiency-related diseases like rickets or osteomalacia, many integrative health experts suggest aiming for higher levels (typically 40–60 ng/mL) to support optimal immune function, bone strength, and mood balance.
This test is widely available through healthcare providers and many direct-to-consumer labs. It’s a simple blood draw and often part of annual wellness screenings.
Testing for Vitamin K
Testing for vitamin K deficiency is more complex. There is no standard test that directly measures vitamin K2 levels in the same way as vitamin D. However, there are indirect markers that can give insight into K status:
- Prothrombin Time (PT): This test measures how long it takes your blood to clot. While it’s most often used to monitor blood-thinning medications, an unusually long clotting time may suggest inadequate vitamin K1.
- Undercarboxylated Osteocalcin and uncarboxylated Matrix Gla-protein (ucMGP): These are emerging biomarkers that reflect functional vitamin K2 status, since K2 activates the proteins responsible for bone mineralization and calcium regulation. However, these tests are not yet widely used in standard medical practice.
Because testing for vitamin K is less accessible, many people focus on maintaining consistent intake through diet or targeted supplementation—especially if they’re in a higher-risk category.
If you're unsure where you stand, talk to a healthcare professional about testing options and how they can support your broader health goals.
Dietary Sources of Vitamin D and K
While supplements can be helpful, nutrition is the foundation of long-term health—and getting vitamins D and K from whole foods is a great place to start. That said, not all sources are created equal, especially when it comes to vitamin K2.
Best Food Sources of Vitamin D
Vitamin D is found in relatively few foods, and even those sources typically offer modest amounts. Some of the most reliable dietary sources include:
- Fatty fish such as salmon, sardines, and mackerel
- Cod liver oil, a traditional source high in vitamin D
- Egg yolks, especially from pasture-raised hens
- Fortified foods like milk, orange juice, and some cereals
However, even a diet rich in these foods may fall short of optimal intake—especially if you have limited sun exposure or absorption issues. This is why many individuals, especially those at higher risk, benefit from targeted supplementation to reach optimal levels.
Best Food Sources of Vitamin K
Vitamin K exists in two primary forms: K1 (phylloquinone) and K2 (menaquinone). They differ in both structure and function, and they come from different dietary sources.
- Vitamin K1 is found mostly in leafy green vegetables, such as spinach, kale, collard greens, and broccoli. It supports healthy blood clotting and is abundant in plant-based diets.
- However, K1 must be converted by beneficial gut bacteria into K2—something that doesn’t always happen efficiently, especially in individuals with poor gut health.
Best Food Sources of Vitamin K2
Vitamin K2 is much harder to obtain from a standard Western diet. It’s mainly found in:
- Fermented foods, like natto (a Japanese soybean dish rich in MK-7)
- Grass-fed animal products, including butter, cheese, and egg yolks and 100% grass-fed beef
- Liver and other organ meats
- Hard cheeses and full-fat dairy—especially from 100% grass-fed animals
Because modern diets often lack these traditional foods, K2 intake tends to be low for many individuals. Prioritizing these nutrient-dense sources—or supplementing strategically—can help fill in the gaps and support both bone and cardiovascular health.
Supplementing Vitamin D and K: What You Need to Know
For many people, getting enough vitamins D and K from diet and sunlight alone simply isn’t realistic—especially in today’s fast-paced, mostly indoor lifestyle. That’s where supplementation comes in. When used appropriately, high-quality supplements can help you bridge the nutritional gap and support optimal wellness.
Choosing the Right Form
Vitamin D3 (cholecalciferol) is, by far, the preferred form for supplementation, as it’s the same type your body naturally produces from sunlight and is more effective at raising and maintaining blood levels compared to D2 (ergocalciferol).
For vitamin K, there are a few options:
- Vitamin K1 (phylloquinone) supports blood clotting.
- Vitamin K2, particularly the MK-7 and MK-4 forms, is ideal for bone and cardiovascular support.
- MK-7 has a longer half-life in the body, making it useful for consistent, sustained benefits.
- MK-4 is shorter-acting but still beneficial—especially when combined with MK-7 for full-spectrum support.
- (We suggest finding a supplement with both MK4 & MK7 forms)
Look for MK-7 in the all-trans form, which is bioactive and nature-identical. Some inferior supplements contain a mixture of trans and cis forms, reducing efficacy.
Absorption Matters
Because both D and K are fat-soluble, they require dietary fat for proper absorption. Taking them with a meal that contains healthy fats can enhance bioavailability.
For maximum absorption, consider a liquid liposomal supplement, which helps nutrients bypass digestion and deliver directly into cells. Liposomal D3 + K2 supplements can offer superior uptake—especially for those with gut or absorption issues.
The Power of Pairing D3 and K2
Taking vitamin D3 with K2 offers synergistic benefits. While D3 helps your body absorb calcium, K2 ensures it gets directed into the bones and teeth—not soft tissues like arteries. This combination helps support both bone density and cardiovascular health.
Always check labels for clean, high-quality sourcing, and consult your healthcare provider to determine the right dosage for your needs and lifestyle.
Lifestyle and Absorption Factors
When it comes to optimizing vitamin D and K levels, how you live can matter just as much as what you eat or supplement. Several lifestyle and physiological factors influence how well your body produces, absorbs, and utilizes these essential fat-soluble nutrients.
Sun Exposure for Natural Vitamin D Synthesis
The most natural source of vitamin D is sunlight—specifically, UVB rays that trigger vitamin D3 production in the skin. However, a variety of factors can reduce your body’s ability to make enough, including:
- Time of year: In many regions, especially northern latitudes, UVB exposure is too low for meaningful vitamin D production from fall through early spring.
- Time of day: Midday sun is most effective for D3 synthesis.
- Sunscreen use and clothing: These block UVB rays, preventing the skin from producing vitamin D.
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Skin tone: Individuals with darker skin tones produce less vitamin D in response to sun exposure due to higher melanin content.
Spending just 10–30 minutes in direct sun (without sunscreen) a few times a week can help, depending on your location, skin tone, and time of year.
Gut Health and Vitamin K
Vitamin K1 from plant foods must be converted by beneficial gut bacteria into vitamin K2, particularly MK-7. If your gut microbiome is imbalanced—due to antibiotics, poor diet, or chronic digestive issues—this conversion may be impaired.
Maintaining a healthy gut through fiber-rich foods, fermented foods, and probiotics can support natural K2 production and improve overall nutrient absorption.
Cofactors That Support Vitamin D Metabolism
Several nutrients act as cofactors that enhance vitamin D’s effectiveness, including:
- Magnesium – Required for converting vitamin D into its active form.
- Vitamin A and zinc – Help regulate vitamin D’s immune and gene expression functions.
- Healthy fats – Aid in absorption of both D and K.
Formula Spotlight: Pure TheraPro™ Vegan D3 + K2 Full Spectrum
If you're looking for an easy, effective way to support bone, heart, and immune health, Pure TheraPro’s Vegan D3 + K2 Full Spectrum delivers next-level nutritional support in one clean, high-potency formula.
Liposomal Formula for Maximum Absorption & Efficacy
Our formula features liposomal Vitamin D3 & Vitamin K2, shown in clinical studies to enhance bioavailability and utilization. Liposomal nutrients are absorbed faster and more efficiently, supporting optimal results—even for individuals with compromised digestion or nutrient absorption issues.
We combine two essential forms of K2—MK-4 and MK-7—for broad-spectrum benefits. MK-7 is provided in its all-trans form via MenaQ7®, a patented and clinically studied vitamin K2 ingredient known for its purity and bioactivity. Together with vegan-sourced MK-4, these forms help guide calcium away from arteries and into the bones and teeth, where it belongs.
Clinically Recommended D3 + K2 Synergy
Vitamin D3 supports calcium absorption. Vitamin K2 ensures that calcium gets properly directed to bone and dental tissue. The synergy between these two nutrients is critical—not just for bone density, but also for maintaining arterial flexibility and cardiovascular health.
Each serving (5 drops) provides 5,000 IU of liposomal D3 and 600 mcg of K2 (MK-4 + MK-7). There are no fillers, excipients, gluten, dairy, soy, corn, or artificial ingredients—just clean, potent nutrients that support your wellness goals.
Purity is Our Priority
At Pure TheraPro™, we never compromise. All of our ingredients are carefully sourced, lab tested, and free from China-origin raw ingredients. We manufacture in the USA and formulate with a focus on clinically studied, practitioner-recommended ingredients to deliver real results.
If you're serious about optimizing your D3 and K2 levels, choose a formula that’s as effective as it is clean—Pure TheraPro™ Vegan D3 + K2 Full Spectrum.
Final Thoughts: Optimizing Your Vitamin D and K Levels
Vitamins D and K are two of the most underappreciated—but vitally important—nutrients when it comes to whole-body wellness. From maintaining strong bones and resilient immunity to supporting cardiovascular health and even mood balance, the impact of these fat-soluble vitamins is wide-reaching.
As we've explored, deficiencies in either D or K can lead to subtle and not-so-subtle symptoms, including fatigue, frequent infections, mood changes, easy bruising, and even increased risk of fractures or arterial calcification. Yet these symptoms often go unrecognized until they start affecting daily life.
The good news? These deficiencies are among the most straightforward to correct with the right strategy. A combination of smart sun exposure, a nutrient-rich diet, and targeted supplementation can help restore balance and support long-term health. Testing your levels—especially for vitamin D—is an easy first step toward understanding your personal needs.
Your body was designed to function beautifully when given the right tools. Vitamin D and K are two of the most powerful tools in that toolbox—and now, you know how to use them wisely.
References
Parva, N. R., Tadepalli, S., Singh, P., Qian, A., Joshi, R., Kandala, H., ... & Cheriyath, P. (2018). Prevalence of vitamin D deficiency and associated risk factors in the US population (2011-2012). Cureus, 10(6), e2741.
Looker, A. C., Johnson, C. L., Lacher, D. A., Pfeiffer, C. M., Schleicher, R. L., & Sempos, C. T. (2011). Vitamin D status: United States, 2001–2006. NCHS Data Brief, (59), 1-8.
Centers for Disease Control and Prevention. (2023). About Vitamin K Deficiency Bleeding.
Centers for Disease Control and Prevention. (2011). Vitamin D Status: United States, 2001–2006. NCHS Data Brief, (59), 1-8.
U.S. Preventive Services Task Force. (2021). Screening for Vitamin D Deficiency in Adults: US Preventive Services Task Force Recommendation Statement. JAMA, 325(14), 1436–1442.
American Academy of Pediatrics. (2022). Vitamin K and the Newborn Infant. Pediatrics, 149(3), e2021056036.