Last reviewed October 28, 2026 by the Cellovi team.
The short answer
Vitamin D3 helps your body absorb calcium. Vitamin K2 activates the proteins that put that calcium to work in bone. Each has a well-established role in bone health; research on the two together is growing. Cellovi D3 + K2 is a higher-potency formula: 5,000 IU of D3 and 100 mcg of K2 as MK-7 in one capsule. That is above the 4,000 IU (international units) daily upper limit set for adults. Below, we explain what that limit means and who a higher amount suits.*
Our grade: Established for the roles of vitamins D and K in normal bone. Growing for the two taken together. Frontier for heart health from K2.
Vitamin D3: the absorber
Vitamin D lets your gut absorb calcium and phosphorus and keeps blood calcium in its normal range, which bone needs to stay strong (NIH Office of Dietary Supplements). Few foods contain much of it: 94% of Americans get less than 400 IU a day from food, and about 18% are at risk of inadequate blood levels.
- D3 or D2? D3 (cholecalciferol) raises blood vitamin D more than D2 does (NIH ODS).
- Take it with a meal that has some fat. Breakfast is the easiest one to remember. The label suggests 20 to 30 minutes before a meal; what matters most in the research is that the meal has some fat. In one study, D3 taken with a meal containing fat raised blood levels 32% more than the same dose with a fat-free meal (Dawson-Hughes et al., 2015).
Vitamin K2: the director
Vitamin K switches on proteins that bind calcium. Two matter here: osteocalcin, made in bone, and matrix Gla protein, found in cartilage and blood vessel walls (NIH ODS).
- K1 or K2? K1 comes mainly from leafy greens. K2 comes in several forms; MK-7 stays in the body much longer, gives steadier levels with daily use, and activated osteocalcin more completely than K1 in one study (Schurgers et al., 2007).
- A 3-year trial: 244 healthy women aged 55 to 65 took 180 mcg of MK-7 or placebo. The MK-7 group lost less bone mineral density with age at the lower spine and the femoral neck of the hip (Knapen et al., 2013).*
- Heart health: in the same women, arteries stayed more flexible with MK-7 than with placebo (Knapen et al., 2015).*
- There is no upper limit for vitamin K, because of its low potential for harm (NIH ODS).
Why take them together
The two work in sequence. Vitamin D increases the production of vitamin K-dependent proteins, and those proteins need vitamin K to become active (van Ballegooijen et al., 2017). The mechanism is well described. Trials of the pair together are building, led by research in women over 50, which is why we grade the pairing Growing.*
Healthy aging research. In a 4-year substudy of the large VITAL trial (1,031 adults aged 50 and over), those randomized to 2,000 IU of vitamin D3 a day lost less telomere length, the protective caps on chromosomes that shorten with age, than those on placebo (Zhu et al., 2025).*
How much D3 to take
| Adults | Vitamin D per day |
|---|---|
| Recommended intake, ages 19 to 70 | 600 IU (15 mcg) |
| Recommended intake, 71 and over | 800 IU (20 mcg) |
| Tolerable upper intake level (UL) | 4,000 IU (100 mcg), from all sources |
| Cellovi D3 + K2, one capsule | 5,000 IU (125 mcg) |
| Where toxicity becomes a concern | Unlikely below 10,000 IU (250 mcg) a day |
Source: NIH ODS, based on the National Academies' 2011 report.
What the upper limit means. The UL is not a danger line, and it is not a target. It is the highest amount, from food, fortified foods and supplements together, that is unlikely to cause harm in nearly everyone who takes it every day, long term, without medical supervision. Doctors sometimes recommend more than the UL for a period of time, for example to bring a low level back up (NIH ODS).
Who a higher-potency formula suits. Adults who get little sun or know their blood level is low, and anyone whose clinician has suggested more than a standard dose. Vitamin D does its most important work where intake or levels are low.
How levels build. Blood vitamin D builds slowly: its main blood form has a half-life of about 15 days, so levels settle over roughly 2 to 3 months of daily use. For reference, this is how a 25(OH)D blood result is read:
| Blood 25(OH)D | What it means |
|---|---|
| Below 12 ng/mL | Deficient |
| 12 to 19 ng/mL | Inadequate for bone and overall health |
| 20 ng/mL and above | Adequate for most people |
| Above 50 ng/mL | Possible adverse effects; talk to your clinician |
Source: NIH ODS.
If you already take a multivitamin or another product with vitamin D, count it too. If you know your level is already in a good range, ask your clinician whether to keep this dose or take it every other day.
Who should check with a doctor first
- Warfarin or other blood thinners: MK-7 at 50 mcg a day or more may change how these medicines work (Schurgers et al., 2007). Do not start without your doctor.
- Thiazide diuretics, which together with vitamin D can raise blood calcium too high; steroids such as prednisone; and orlistat (NIH ODS).
- Kidney disease, sarcoidosis or other granulomatous conditions, a parathyroid disorder, or a history of high calcium or kidney stones.
- Anyone pregnant, breastfeeding or under 18.
Signs of too much vitamin D include nausea, vomiting, muscle weakness, confusion, and unusual thirst or urination. If you notice them, stop and see a doctor.
Each capsule also contains 210 mg of calcium, a modest share of the 1,000 to 1,200 mg adults need a day from all sources (NIH ODS), and black pepper extract.
How to take it
- 1 capsule a day with breakfast or another meal that has some fat.
- Same time every day. This is a routine measured in months, not days.
See Vitamin D3 + K2. It is part of Her Healthspan, with Creatine and Magnesium Glycinate.*
Common questions
Is 5,000 IU of vitamin D3 too much?
It is above the 4,000 IU daily upper limit for adults. That limit is not a danger line: it is the highest amount unlikely to cause harm in nearly everyone who takes it long term without medical supervision, and toxicity is unlikely below 10,000 IU a day. A higher amount suits adults who get little sun or know their level is low; if your level is already good, ask your clinician whether to keep this dose or take it every other day.
When should I take vitamin D3 and K2?
With breakfast or another meal that has some fat. In one study, D3 taken with a meal containing fat raised blood levels 32% more than with a fat-free meal.
How long does it take to raise vitamin D levels?
Blood vitamin D builds slowly. Its main blood form has a half-life of about 15 days, so levels settle over roughly 2 to 3 months of daily use.
Can I take D3 + K2 with a blood thinner?
Do not start without your doctor. MK-7 at 50 mcg a day or more may change how warfarin and other blood thinners work.
Sources
- NIH Office of Dietary Supplements. Vitamin D: fact sheets for health professionals and consumers.
- NIH Office of Dietary Supplements. Vitamin K: fact sheet for health professionals.
- NIH Office of Dietary Supplements. Calcium: fact sheet for health professionals.
- Institute of Medicine (National Academies). Dietary Reference Intakes for Calcium and Vitamin D, 2011.
- Dawson-Hughes B et al. Dietary fat increases vitamin D-3 absorption. Journal of the Academy of Nutrition and Dietetics, 2015.
- Schurgers LJ et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood, 2007.
- Knapen MHJ et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 2013.
- Knapen MHJ et al. Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women. Thrombosis and Haemostasis, 2015.
- van Ballegooijen AJ et al. The synergistic interplay between vitamins D and K for bone and cardiovascular health: a narrative review. International Journal of Endocrinology, 2017.
- Zhu H et al. Vitamin D3 and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and Omega-3 TriaL (VITAL) randomized controlled trial. American Journal of Clinical Nutrition, 2025.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.