Vitamin D3 + K2 - synergy for strong bones & immune system

Synergy of vitamin D3 and K2 - basics

Vitamin D3 (cholecalciferol) and vitamin K2 (menaquinone) are fat-soluble vitamins that play different but interrelated roles in human metabolism. Vitamin D3 is either formed through the skin when exposed to sunlight or absorbed through foods such as fatty fish and mushrooms and converted to 25-hydroxyvitamin D in the liver. In the kidneys, this produces the hormonally active form 1,25-dihydroxyvitamin D, which regulates calcium and phosphate absorption in the intestine and thus influences bone growth and mineral balance. Vitamin K2 is a generic term for various menaquinones (MK-4 to MK-13) and is found in foods such as fermented soy (natto), fermented dairy products and meat from grazing animals. Vitamin K2 activates γ-carboxyglutamate (Gla)-containing proteins, including osteocalcin and the matrix Gla protein (MGP), by carboxylating these proteins. This enables them to bind calcium and store it in bone tissue. Without sufficient vitamin K2, these proteins remain undercarboxylated and cannot fulfill their role.

Recent research shows that vitamin D3 and K2 have a synergistic effect. Vitamin D stimulates the production of vitamin K-dependent proteins, which are important for calcium binding in bones and blood vessels, while vitamin K enables their activation. A review in the International Journal of Endocrinology describes that vitamin D stimulates the formation of osteocalcin and MGP; these proteins must be carboxylated by vitamin K2 in order to bind calcium properly[0]. Without this carboxylation, calcium can be deposited in blood vessels and increase the risk of atherosclerosis. Understanding this interaction forms the basis for the following detailed discussion.

Why a balanced supply is important

Vitamin D deficiency is widespread in Central Europe. A recent cross-sectional study of top German athletes found that 55.5% of athletes had an insufficient 25-hydroxyvitamin D level (< 30 ng/ml) and 16% even had a deficiency (< 20 ng/ml). According to the same study, 61.5% of adults in the general German population have a 25(OH)D level below 20 ng/ml. Vitamin D deficiency is associated with an increased risk of osteoporosis, muscle weakness and infections. Vitamin K deficiency is considered less common, but can occur due to an unbalanced diet, chronic liver disease or long-term antibiotic therapy. Undercarboxylated osteocalcin in serum serves as a marker for vitamin K deficiency and is associated with increased bone fragility.

Vitamin D requirements depend on age, body weight, skin type, sun exposure and individual factors. A workshop report recommends a daily intake of 20 µg (800 IU) for people aged 65 and over to achieve 25(OH)D levels above 75 nmol/l[3]. According to the same recommendations, adults need 10-20 µg (400-800 IU) per day to maintain 25(OH)D levels of 50-75 nmol/l, with a higher requirement often occurring in winter[4]. Studies investigating synergistic effects usually use doses of 45-180 µg MK-7 or 45 mg menatetrenone (MK-4).

Risk groups for vitamin D and K deficiency

• Older people and people with dark skin color: The skin's ability to produce vitamin D decreases with age and dark pigmentation. At the same time, the risk of osteoporosis and cardiovascular disease increases.
• People who get little sunlight: Office workers, residents of northern latitudes or people who wear religious clothing cannot sufficiently activate their vitamin D synthesis. In such cases, supplementation can help to cover the requirement.
• Vegans and vegetarians: Vitamin D3 is mainly found in animal foods such as fatty fish and eggs. Vegan alternatives such as mushrooms and fortified plant milks often contain vitamin D2. Vitamin K2 is found in fermented foods (natto, matured cheese); those who do not eat these regularly could develop a deficiency.
• People with malabsorption: Chronic inflammatory bowel disease, coeliac disease, liver or biliary tract disease and long-term use of certain medications (e.g. antibiotics, cholestyramine) can impair the absorption of fat-soluble vitamins.
• Pregnant women and breastfeeding mothers: Vitamin D requirements increase during pregnancy and breastfeeding to support the child's development. However, individual recommendations apply - excessive doses should be avoided.

People in these groups should have their serum levels of vitamin D and, if necessary, vitamin K determined and discuss with their doctor whether supplementation is advisable. Overdosing can lead to hypercalcemia; therefore supplements should be used responsibly.

Vitamin D3 - structure, metabolism and functions

Vitamin D3 is a prohormone that is produced in the skin from 7-dehydrocholesterol under the influence of UV-B light. Over 80-90% of the vitamin D requirement is covered by endogenous synthesis, the rest comes from food. In the blood, vitamin D is bound to a binding protein (VDBP) and hydroxylated in the liver to 25-hydroxyvitamin D (25(OH)D), which serves as a storage form and biomarker. The second hydroxylation to 1,25-dihydroxyvitamin D (calcitriol), which acts as a hormone, takes place in the kidneys. Calcitriol binds to the vitamin D receptor (VDR), which is expressed in numerous tissues, including bone, skeletal muscle and immune cells.

Bone health: Calcitriol increases the expression of transport proteins in the intestine (calbindin), allowing calcium and phosphate to be absorbed more efficiently. Vitamin D also regulates bone remodeling by influencing both osteoblasts (form bone matrix) and osteoclasts (break down bone). A deficiency leads to reduced bone mineral content, rickets in children and osteomalacia in adults. A meta-analysis of eight randomized controlled trials with a total of 971 participants shows that the combination of vitamin D and K significantly increases total bone density and reduces the proportion of undercarboxylated osteocalcin[6]. These results suggest that while vitamin D3 alone brings calcium into the body, vitamin K2 is needed to properly utilize it.

Immune function: The VDR is present in various immune cells, including T cells, B cells, dendritic cells and macrophages. A review from Frontiers in Immunology explains that the active form of vitamin D promotes a tolerogenic immune response and modulates both innate and adaptive immune responses[7]. Vitamin D deficiency is associated with an increased risk of autoimmune diseases, infections and chronic inflammation. In a large randomized trial (VITAL trial), a daily vitamin D supplement (2,000 IU) was used; after a median follow-up period of five years, vitamin D reduced the incidence of autoimmune diseases (hazard ratio 0.78)[8]. However, the effect was no longer detectable after discontinuation of the preparation two years later. This underlines the fact that vitamin D3 can modulate the immune system, but is not a cure.

Muscle function and sport: Vitamin D is also associated with muscle strength and performance. In a retrospective study of older people, daily intake of vitamin D3 over several months led to a significant increase in 25(OH)D levels and an improvement in muscle strength in the lower extremities and hand strength[9]. Athletes with low vitamin D levels are more susceptible to stress fractures and infections, which is why an adequate supply - ideally through sun exposure and, if necessary, nutritional supplements - is important for people who are active in sports.

Vitamin K2 - forms, function and importance

Vitamin K exists in two main forms: Vitamin K1 (phylloquinone) and vitamin K2 (menaquinone). Vitamin K1 comes mainly from green leafy vegetables such as spinach, cabbage and broccoli and contributes to blood clotting. Vitamin K2 comprises a family of menaquinones (MK-4 to MK-13) and is found in fermented foods (natto, sauerkraut, mature cheese) and animal products (liver, egg yolk). MK-4 is converted from vitamin K1 in certain tissues, while MK-7 to MK-10 are often of bacterial origin.

Activation of Gla proteins: Vitamin K2 is a necessary cofactor for the carboxylation of Gla proteins. These include osteocalcin, which transports calcium into the bone matrix, and the matrix Gla protein (MGP), which prevents calcium deposits in blood vessel walls. Without carboxylation, these proteins remain in an inactive state, which can lead to reduced bone stability and increased vascular calcification. A systematic review from 2022 concluded that vitamin K2 improves bone mineral density in postmenopausal women and reduces fracture rates; a combination with vitamin D3 and/or calcium led to significantly better results than vitamin K2 alone[10].

Different forms of menaquinone: MK-7 has a longer half-life in plasma (about 2-3 days) than MK-4, which means that a daily intake of low doses may be sufficient. MK-4 is often used in higher doses (45 mg) as its plasma half-life is only a few hours. A randomized, double-blind study with postmenopausal women investigated the intake of MK-7 (375 µg/day) over three years in combination with vitamin D3 (38 µg/day) and calcium (800 mg/day). The amount of undercarboxylated osteocalcin decreased significantly in the MK-7 arm, but bone density did not differ from the placebo group[11]. This shows that although MK-7 improves the carboxylation of osteocalcin, administration alone may not be sufficient to increase bone density.

Cardiovascular effects: Matrix Gla protein (MGP) is a potent inhibitor of vascular calcification. A narrative review in Open Heart highlights that vitamin K2 promotes the activation of MGP and is associated with a reduction in arterial stiffness and slowed vascular and valvular calcification[12]. A lack of active MGP increases the deposition of calcium in blood vessels and could increase the risk of cardiovascular disease. However, it should be noted that most of the evidence to date comes from observational studies; randomized controlled trials are still pending. Such associations have therefore not yet been confirmed by the European Food Safety Authority (EFSA). Further studies are required.

Synergy of vitamin D3 and K2: Scientific evidence

The synergy between vitamin D3 and K2 is based on the fact that both vitamins intervene at different but complementary points in the calcium metabolism. Vitamin D promotes the absorption of calcium and the synthesis of osteocalcin and MGP, while vitamin K2 enables their activation. Without vitamin K2, an increased vitamin D level would lead to an increased formation of inactive proteins that cannot incorporate calcium into the bone. Numerous studies are therefore investigating the combined intake of both vitamins:

• Meta-analysis on vitamin D and K: A systematic review in the journal Food & Function (2020) analyzed eight randomized controlled trials with a total of 971 participants. The authors reported that the combination of vitamin D and K significantly increased total bone density and greatly reduced the proportion of undercarboxylated osteocalcin, especially when vitamin K2 (MK-7) was used[13]. This result suggests that the synergistic effect is based on the improvement of protein activation and calcium storage in bone.
• Prospective study on spinal fusion: A clinical study published in May 2025 examined 71 osteoporotic patients after minimally invasive spinal fusion. The test group received vitamin K2 (45 mg/day), vitamin D3 (250 IU/day) and calcium (1.2 g/day), the control group only vitamin D3 and calcium. After six months, the fusion rate was significantly higher in the combination group (91.67% vs. 74.29%) and the bone formation marker P1NP increased more significantly[14]. This suggests that vitamin K2 may promote bone healing after surgery, although the study was not randomized and further research is needed.
• Korean study in postmenopausal women: In a six-month randomized controlled trial of postmenopausal women, 38 participants received daily vitamin K2 (menatetrenone, 15 mg three times daily), vitamin D (400 IU) and calcium; the control group received only vitamin D and calcium. The L3 bone density increased significantly in the vitamin K group, while it decreased slightly in the control group. At the same time, the serum level of undercarboxylated osteocalcin decreased significantly more in the vitamin K group[15].
• Cross-sectional study with 8,216 participants: A review paper in Current Research in Nutrition and Food Science examined twelve studies (five RCTs, six observational studies, one quasi-experimental design) with a total of 8,216 participants. Eleven of these studies showed a synergistic effect of vitamin D and K on improving bone mineral density, reducing fractures and improving cardiovascular markers[16]. The authors emphasized that vitamin D and K are mutually reinforcing, which is relevant for the prevention of osteoporosis and arteriosclerotic diseases.
• Randomized placebo-controlled MK-7 study: In a three-year study of 142 postmenopausal women with osteopenia, all participants received vitamin D3 (38 µg/day) and calcium (800 mg/day). In addition, the verum group received 375 µg MK-7 daily. After one year, the proportion of undercarboxylated osteocalcin decreased significantly more in the MK-7 group (-65.2 % vs. -0.03 % in the placebo group), but over three years there was no difference in bone mineral density between the groups[17]. This emphasizes that MK-7 improves the activation of osteocalcin but is not necessarily sufficient on its own to increase bone density if vitamin D and calcium supplementation is already adequate.

In summary, these studies show that taking vitamin D3 and K2 together improves bone mineralization and reduces the proportion of inactive osteocalcin molecules. At the same time, initial studies indicate benefits for cardiovascular health and bone healing. However, dosages, study duration and populations studied vary greatly; the results cannot therefore be directly applied to all population groups. For use in humans, it is important to adhere to the dosage recommendations and not to make any promises of a cure.

Calcium, vitamin D3 and K2: a combination for strong bones

Calcium is the most abundant mineral in the human body and, together with phosphate, forms the structure of bones. Adequate calcium intake in the diet - for example through dairy products, nuts, seeds (sesame, almonds), green vegetables and mineral water - is a prerequisite for a stable bone matrix. However, without sufficient vitamin D, only a small proportion of the calcium ingested can enter the bloodstream. Vitamin D3 increases the formation of calbindin in the intestine and thus increases calcium absorption. The additional administration of vitamin K2 ensures that the absorbed calcium is incorporated into the bones and not transported into the blood vessel walls.

A meta-analysis in the Journal of Orthopaedic Surgery and Research examined the combined effect of vitamin K and calcium on bone health. The authors analyzed seven randomized controlled trials and found that vitamin K together with calcium increased lumbar vertebral bone density and decreased undercarboxylated osteocalcin more than calcium alone[18]. Interestingly, this effect was particularly pronounced when vitamin K2 was used. Another meta-analysis emphasizes that the combination of vitamin D, K and calcium has a particularly positive effect on bone strength and can prevent osteoporosis[19]. These synergistic effects can be explained physiologically: Vitamin D ensures the provision of calcium, vitamin K activates osteocalcin, and calcium serves as a building material.

Nevertheless, it should be noted that supplements alone are no substitute for a balanced diet. A calcium-rich diet, sufficient sun exposure, physical activity (especially strength training and moderate endurance training) and a healthy lifestyle are the cornerstones of bone health. People who get enough calcium from their diet and exercise regularly outdoors can increase their vitamin D synthesis and often need fewer supplements. However, if a deficiency is diagnosed or in at-risk groups, a targeted intake of vitamin D3 and K2 can be useful.

Effects on the cardiovascular system

In addition to its role for the bones, the interaction of vitamin D3 and K2 also plays a potentially important role for vascular health. Arterial calcification is regulated by matrix Gla protein (MGP), among other things. This protein binds calcium in the vessel walls and thus prevents crystallization and deposition in the arteries. The activation of MGP is vitamin K-dependent. Without sufficient vitamin K, MGP remains uncarboxylated and therefore inactive - calcium can be deposited more easily in the vessels. A review in the journal Open Heart emphasizes that vitamin K2 promotes the activation of MGP and thus reduces arterial stiffness and could lead to slower calcification of vessels and heart valves[20]. The authors refer to studies in which an increased intake of vitamin K2 correlates with lower cardiovascular mortality. However, it should be noted that causal evidence from randomized clinical trials is still lacking. These correlations have therefore not yet been confirmed by the EFSA and further studies are required to derive specific recommendations.

Vitamin D also influences the cardiovascular system, among other things by regulating the renin-angiotensin system, blood pressure and inflammatory processes. Vitamin D deficiency has been associated with hypertension, heart failure and myocardial infarction; however, no clear benefit of high-dose supplementation has been found in clinical trials. Most of the positive observations come from epidemiological studies, while randomized trials such as the VITAL trial did not show a significant reduction in cardiovascular events with vitamin D supplements. In summary, it can be said that an adequate supply of vitamin D and K can contribute to the maintenance of normal cardiovascular function, but a therapeutic effect has not yet been proven.

Influence on the immune system and inflammation

Vitamin D3 modulates the innate and adaptive immune system. Calcitriol binds to VDRs on dendritic cells and prevents their complete maturation; this promotes the differentiation of regulatory T cells and inhibits inflammatory T helper cells. Vitamin D also increases the expression of antimicrobial peptides (e.g. cathelicidin) that fight bacteria and viruses. The aforementioned Frontiers in Immunology reviewemphasizes that a sufficient vitamin D level leads to a more tolerogenic immune response and thus reduces excessive inflammatory reactions[21]. The relationship between vitamin D status and susceptibility to infection has been intensively discussed during the COVID-19 pandemic, but the evidence is mixed. A balanced supply is recommended to support the normal function of the immune system.

Vitamin K2 also has immunomodulatory properties, but these are less well understood. Some studies suggest that vitamin K has anti-inflammatory effects by inhibiting NF-κB signaling and reducing oxidative stress responses. In addition, vitamin K is required for the synthesis of protein S, which plays a role in the coagulation cascade and the complement system. A possible synergistic effect of vitamin D3 and K2 could lie in the control of inflammatory processes, but there is currently a lack of solid clinical data on this. These relationships have not yet been confirmed by the EFSA; further studies are required.

Dosage and safe use of vitamin D3 & K2

The correct dosage is crucial to achieve benefits and avoid risks. Most studies observing synergistic effects use moderate doses of vitamin D between 400 and 2 000 IU per day, sometimes supplemented by an initial dose (loading dose) to achieve a rapid increase in 25(OH)D levels. The workshop report mentioned above summarizes that 1 µg (40 IU) of vitamin D per day increases the serum concentration of 25(OH)D by about 1 nmol/l[22]. According to this report, 20 µg (800 IU) per day is often required to ensure a 25(OH)D level above 75 nmol/l, taking into account individual factors such as body weight, baseline levels and genetic variations. Above 100 µg (4,000 IU) per day, adults should only take vitamin D under medical supervision, otherwise there is a risk of hypercalcemia.

There are no generally valid reference values for vitamin K2. Doses between 45 µg (MK-7) and 45 mg (MK-4) are used in clinical studies. The Japanese standard dosage of menatetrenone (MK-4) for osteoporosis prophylaxis is 45 mg per day. Products with MK-7 usually contain 50-200 µg per capsule. Due to the longer half-life of MK-7, a daily intake is sufficient. For people taking anticoagulants from the vitamin K antagonist group (e.g. warfarin), supplementation with vitamin K2 must be agreed with the doctor treating them, as it can influence the effectiveness of the medication.

The following points should be observed for safe use:

• The dosage should be selected individually and in consideration of serum levels, lifestyle and diet.
• Vitamin D is a fat-soluble vitamin; therefore it should be taken with a meal containing fat to improve absorption.
• Vitamin K2 should also be taken daily for optimal effect. Higher doses are required for MK-4 as it is broken down more quickly.
• Pregnant women, nursing mothers, children and people with chronic illnesses should consult a doctor before taking supplements.
• Too much calcium, vitamin D or K can have side effects. Symptoms of hypercalcemia include nausea, vomiting, frequent urination and cardiac arrhythmias.

Natural sources of vitamin D3 & K2

A balanced diet remains the basis for the supply of micronutrients. The following sources are suitable for vitamin D3:

• Sunlight: 15-30 minutes of uncovered skin (face, arms, legs) between 11 am and 3 pm is sufficient to cover the vitamin D requirement in summer. In winter, UV-B radiation is lower in Germany, which is why supplements can be useful.
• Fatty fish: Salmon, mackerel, herring and sardines provide up to 20 µg of vitamin D3 per 100 g. Cod liver oil is also rich in vitamin D.
• Eggs and dairy products: Egg yolk contains moderate amounts of vitamin D; some dairy products are fortified with vitamin D.
• Mushrooms: Certain types of mushrooms (e.g. button mushrooms) grown under UV light contain relevant amounts of vitamin D2, which is less efficient in the body than D3, but contributes to overall synthesis.
• Fortified foods: Plant-based milk, margarine and breakfast cereals are often fortified with vitamin D. Vegan products should look for D3 from algae (vegan).

The following foods are recommended for vitamin K2:

• Natto: Fermented soybeans are one of the richest sources of MK-7. One serving (50 g) can contain up to 500 µg of vitamin K2.
• Fermented dairy products: Matured cheese (Brie, Gouda, Edam), kefir and yoghurt contain MK-8 and MK-9. The longer the maturing process, the higher the vitamin K2 content.
• Meat and organ meats: Liver, heart and other offal from grazing animals in particular contain MK-4.
• Eggs from free-range hens: Eggs from free-range hens contain higher amounts of vitamin K2 than eggs from caged hens, as the hens eat more green feed.
• Fermented vegetables: Sauerkraut and kimchi provide moderate amounts of vitamin K2. However, the levels are variable and lower than in natto.

If you eat these foods infrequently, you can use food supplements, but you should still make sure you eat a varied diet.

Supplementation: advantages and disadvantages of capsules and tablets

If you cannot fully cover your vitamin D3 and K2 requirements through diet and sunshine, you can take dietary supplements. Products are available in the form of drops, capsules or tablets. They differ in their dosage, the type of menaquinone used and the carrier substance. When choosing a product, attention should be paid to quality, purity and the right balance of vitamins. For vegans, there are preparations with vitamin D3 from lichen or algae and vitamin K2 from fermented plants.

The combination of vitamin D3 and K2 in one preparation is practical, as the ratio of vitamins is balanced. One example is optimal vitamin D3 + K2 tablets, which provide a moderate amount of vitamin D3 and MK-7 per daily portion. Such combination preparations are particularly suitable for people who cannot eat a balanced diet or who suffer from increased requirements. Nevertheless, they should be seen as a supplement to a healthy lifestyle and not as a substitute.

Here you can find our product: XTRA FUEL Vitamin D3 + K2 Tablets

Testimonials and tips for use

Numerous people report positive experiences with the combination of vitamin D3 and K2. Users state that they feel more energetic in winter, get fewer colds and their bone health improves. However, subjective experiences are no substitute for scientific evidence. If you decide to take a supplement, consider the following tips:

• Have your values determined: A blood test is useful to know your baseline 25(OH)D level before you start taking it. Markers for vitamin K supply (e.g. uncarboxylated osteocalcin) can also be measured.
• Time of intake: Vitamin D3 and K2 should be taken with a meal that contains some fat so that the fat-soluble vitamins are optimally absorbed.
• Combination with magnesium: Magnesium is a cofactor of many enzymes in vitamin D metabolism. An adequate supply of magnesium can support the effect of vitamin D3.
• Exercise: Regular physical activity stimulates bone metabolism. Strength training and impact loads (e.g. climbing stairs) increase bone density.
• Long-term use: Vitamin D levels decrease within weeks of stopping the supplements. Long-term, moderate doses are therefore more effective than high short-term doses.

Daily intake in small doses is considered by experts to be better tolerated than sporadic high-dose preparations. If you have any questions about dosage or interactions, you should contact your doctor or pharmacist.

Vitamin D3 and K2 in the context of sport

Stable bone health is essential for athletes to prevent injuries. Vitamin D supports muscle contraction, coordination and regeneration after training, while vitamin K2 stabilizes bone density. The study on top German athletes cited above not only showed a high proportion of insufficient 25(OH)D levels, but also a positive correlation between vitamin D status and hand strength. Athletes in indoor sports or with intensive indoor training schedules (e.g. gymnastics, swimming, basketball) are particularly at risk as they receive less sunlight. A balanced diet, targeted supplementation and regular check-ups can help to optimize vitamin D status and improve performance.

Reports on the synergistic effect of vitamin D3 and K2 in sports are still rare. However, since the activation of osteocalcin and MGP plays a role in muscle strength and energy metabolism, it is conceivable that the combination also supports muscle performance. This hypothesis is based on physiological mechanisms, but has not yet been proven by randomized sports studies. Athletes should therefore follow the usual dietary recommendations and plan the intake of supplements in consultation with sports physicians.

Vitamin D3, K2 and the psyche

In addition to their well-known effects on bones and circulation, vitamin D3 and K2 are increasingly associated with mental health. Vitamin D receptors are also found in the brain; calcitriol influences the synthesis of neurotrophic factors, serotonergic neurotransmitters and the sleep-wake rhythm. Low vitamin D levels are associated with depression, seasonal affective disorder and cognitive impairment. However, randomized studies show inconsistent results: Some studies report a slight improvement in depressive symptoms with vitamin D supplementation, while others find no effect. It is therefore still unclear to what extent vitamin D3 plays a direct role in the psyche.

Vitamin K2 could have neuroprotective properties, as certain menaquinones have an antioxidant effect and promote the synthesis of sphingolipids. However, the evidence is sparse and comes mainly from in vitro studies. Clinical studies investigating the effect of vitamin K2 on mood or cognitive functions are still pending. This topic therefore remains an exciting field of research, but requires caution when it comes to interpretation.

Preventing osteoporosis - what you should consider

Osteoporosis is a systemic skeletal disease characterized by reduced bone mass and deterioration of the microarchitectural bone structure. It increases the risk of fractures, particularly in the spine, hip and wrist. Prevention involves several components:

• Calcium-rich diet: 1 000-1 200 mg of calcium should be consumed daily via dairy products, green vegetables, nuts or mineral water.
• Vitamin D3 and K2: Adequate intake supports calcium absorption and utilization. As described, the combination increases bone density more than the individual doses[24]24}.
• Physical activity: Resistance and strength training in particular improves bone density. Just 30 minutes of brisk walking per day contributes to bone health.
• Avoiding nicotine and moderate alcohol consumption: Smoking and excessive alcohol consumption promote bone loss.
• Hormone replacement therapy: Hormone replacement therapy can be considered for postmenopausal women, but should be weighed up on an individual basis. Vitamin D3 and K2 can be used as supportive measures.
• Regular bone densitometry: Bone densitometry (DXA) is recommended for people at risk (women aged 65 and over, men aged 70 and over, people with chronic corticosteroid use) in order to detect osteopenia at an early stage.

Food supplements with vitamin D3 and K2 can be part of a holistic osteoporosis prevention program. The EFSA allows the following health claims: "Vitamin D contributes to the maintenance of normal bones" and "Vitamin K contributes to normal blood clotting and the maintenance of normal bones". Claims such as "prevents osteoporosis" are not permitted.

Sustainable lifestyle and future prospects

Health care goes beyond the intake of individual vitamins. A balanced diet, regular exercise, stress management and sufficient sleep are the cornerstones of a strong immune system and healthy bones. Vitamin D3 and K2 can complement this lifestyle by optimizing calcium absorption and supporting the balance between bones and blood vessels.

Research on vitamin D3 and K2 is progressing rapidly. In particular, the role of vitamin K2 in vascular health and the potential benefits for the immune system are being studied intensively. Future randomized long-term studies will show whether the observations from animal and observational studies can be translated into concrete health benefits for humans. Until then, the recommendation remains to stick to the current reference values and to consider supplements as a supplement to a healthy lifestyle.

Conclusion

Vitamin D3 and vitamin K2 are two essential fat-soluble vitamins whose interaction is crucial for bone health. Vitamin D3 ensures that calcium is absorbed from the intestine and transported to the bones; vitamin K2 activates proteins such as osteocalcin and MGP, which incorporate calcium into the bones and protect against deposits in the blood vessels. Studies show that the combination of both vitamins improves bone density, supports healing after bone surgery and may contribute to cardiovascular health[25][26]. At the same time, there is evidence of immunomodulatory effects and an influence on muscle strength[27][28].

Despite promising results, some questions remain unanswered. The optimal dosage, the duration of intake and the long-term effects on different population groups require further research. Overdosing can cause undesirable side effects, which is why supplementation should be individually adjusted. Above all, it should be emphasized that vitamin D3 and K2 are not drugs and should not be used to treat diseases. They contribute to the maintenance of normal bones, normal muscle function and normal blood clotting as part of a healthy lifestyle, as permitted by the EU Health Claims Regulation.

The combination of vitamin D3 and K2, embedded in a balanced diet and regular exercise, can be a valuable building block for strong bones, a healthy immune system and an overall better quality of life.

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