Does vitamin D prevent me from breaking bones?

Vitamin D alone does not work well enough. A meta-analysis of nearly 50,000 participants showed that supplementation with vitamin D alone barely reduced the risk of fractures compared with a placebo, including hip fractures¹. Vitamin D without calcium also has virtually no effect on bone density, with one minor exception². Broadly supplementing without a demonstrable deficiency therefore appears to offer little benefit.

The combination of vitamin D and calcium does make a difference. Two large meta-analyses show: 6-15% fewer fractures overall and 16-30% fewer hip fractures¹,³. This applied at approximately 400-800 IU of vitamin D per day plus 1000-1200 mg of calcium per day.

Population studies show that people with higher vitamin D blood levels suffer fewer bone fractures: for each step up in blood level there is a 7% lower risk of a fracture and a 20% lower risk of a hip fracture¹. However, this is not proof of cause and effect; people with higher blood levels may also live healthier lives in other ways.

Supplementation is most worthwhile if you have a demonstrable deficiency or an elevated fracture risk, such as older adults and people in nursing homes. In these groups the combination of calcium and vitamin D works best⁴,⁵. Without a deficiency and without elevated risk, the benefit is far less clear.

Clinical guidelines for osteoporosis list vitamin D as a supportive measure alongside medication, adequate calcium intake, fall prevention and physical activity⁶,⁷. If you actually have osteoporosis, vitamin D is not a substitute for proven medications.