What vitamin should I take with vitamin D (Vit D)?

Vitamin D Should Be Taken With Calcium and Vitamin K

When taking vitamin D, you should take it with calcium (1,200 mg daily for adults, especially elderly women) and consider adding vitamin K (particularly K2) for optimal bone and cardiovascular health.

Primary Co-Supplementation: Calcium

Calcium supplementation is mandatory alongside vitamin D for fracture prevention, particularly in elderly individuals and those at risk for osteoporosis 1. The evidence is clear:

• Take 1,200 mg of elemental calcium daily, divided into doses of no more than 500-600 mg for optimal absorption 1
• Calcium citrate is preferred over calcium carbonate, especially if you take proton pump inhibitors, as it doesn't require gastric acid for absorption 1
• Take calcium with meals to minimize gastrointestinal side effects 1

The rationale is straightforward: vitamin D promotes calcium absorption in the intestines and helps maintain calcium homeostasis between blood and bones 2. Without adequate calcium intake, vitamin D supplementation alone is insufficient for bone health 2. Studies combining vitamin D (800-1000 IU daily) with calcium showed significant reductions in fractures and falls, whereas vitamin D alone showed inconsistent benefits 2.

Secondary Co-Supplementation: Vitamin K

Vitamin K works synergistically with vitamin D for both bone and cardiovascular health 3. The mechanism is compelling:

• Vitamin D promotes production of vitamin K-dependent proteins (like osteocalcin), which require vitamin K for carboxylation to function properly 3
• The combination of vitamin K and D significantly increases total bone mineral density (pooled effect size 0.316) and decreases undercarboxylated osteocalcin 4
• Vitamin K2 at doses less than 500 μg daily, when combined with vitamin D, shows particularly favorable effects on bone density 4

Human intervention studies demonstrate that vitamins K and D work synergistically on bone density, with joint supplementation being more effective than either alone 5, 3. This combination also benefits cardiovascular health by modulating calcium metabolism and preventing vascular calcification 3.

Practical Implementation Algorithm

For general adult supplementation:

• Vitamin D3: 800-1000 IU daily (up to 2000 IU is safe and may be more effective) 1, 6
• Calcium citrate: 500-600 mg twice daily with meals 1
• Vitamin K2 (menaquinone): 100-500 μg daily 4

Timing considerations:

• Vitamin D can be taken at any time of day (fat-soluble, so with a meal containing fat is ideal) 1
• Calcium must be split into two doses and taken with meals 1
• Vitamin K should be taken with a meal containing fat 3

Critical Pitfalls to Avoid

• Do not take vitamin D without calcium if your goal is fracture prevention - the Women's Health Initiative showed that 400 IU vitamin D alone was ineffective, and even caused increased nephrolithiasis when combined with inadequate calcium dosing 2
• Do not exceed 600 mg of calcium per dose - absorption efficiency drops significantly above this amount 1
• Do not use doses below 800 IU of vitamin D daily - lower doses (400 IU) show no fracture reduction benefit 2, 7
• Do not take single mega-doses of vitamin D (≥500,000 IU annually) - these can paradoxically increase falls and fractures 1

Target Monitoring

• Aim for serum 25(OH)D levels of at least 30 ng/mL, with optimal range 30-80 ng/mL 1, 7
• Monitor levels every 1-2 years once target is reached 1
• The combination therapy shows continued benefit up to 44 ng/mL for fracture and fall prevention 2, 7