Does vitamin D prevent me from breaking bones?
Vitamin D alone does not demonstrably reduce the risk of bone fractures. Combined with calcium it does help, especially in older adults and people with a deficiency.
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.
The core consists of two large meta-analyses of randomised trials (PMID 31860103 and PMID 26510847, together approximately 80,000 participants), supplemented by a meta-analysis on bone density (PMID 24119980) and guideline publications (PMID 35478046, PMID 28761958, PMID 38892706, PMID 32972636). The distinction between vitamin D alone versus vitamin D plus calcium is strongly supported; the effects in older adults and nursing home residents are moderately well supported.
What does sunlight do for your bones, apart from vitamin D?
Outside of vitamin D, there is preliminary evidence that red and near-infrared light can directly stimulate bone cells, but this has been demonstrated mainly with controlled light therapy, not with ordinary sunlight. Bear in mind that unprotected exposure to sunlight always carries the risk of skin damage.
Do calcium and vitamin D supplements really help against bone loss?
Calcium and vitamin D together can improve bone density and modestly lower the risk of hip fractures when a genuine deficiency is present. Vitamin D as a standalone supplement does little if your blood levels are already adequate.
How do I know whether I have enough vitamin D, and should I be supplementing?
A blood test (25-OHD) tells you whether you have a deficiency; if your value is below 20 ng/mL, supplementing is worthwhile, especially for your bones. Vitamin D has no proven effect on your heart.
Does drinking a lot of alcohol weaken your bones?
Chronic heavy drinking demonstrably weakens your bones and substantially raises the risk of a hip fracture; for your bones there is no safe level above two drinks per day.
Can a vitamin D deficiency affect your hormones?
A vitamin D deficiency disrupts hormone levels, primarily through a rise in parathyroid hormone PTH, which affects your bones, muscles, and possibly your heart. The effect on sex hormones such as testosterone appears limited, but this has been too little studied to allow firm conclusions.
Can you get too much vitamin D?
Too much vitamin D is genuinely harmful, but that risk only arises at blood levels far above the recommended values. Stick to the dosage on the packaging, and unsure about your level? Have it measured by your GP.