What are the signs of vitamin D deficiency?

In adults, vitamin D deficiency leads to osteomalacia, in which existing bone is incompletely mineralised and weak.

Who is most likely to run low

People with a BMI of 30 or more, and people who have had gastric bypass surgery, tend to have lower vitamin D levels.

What this means for you

Mild vitamin D deficiency usually has no symptoms at all, which is the honest and unsatisfying answer to this question. It is found on a blood test, not in the mirror. Below 30 nmol/L counts as deficient and at least 50 nmol/L is generally considered adequate.

When it goes far enough to produce symptoms, they are skeletal. In children the result is rickets: soft bones, bowed legs, delayed growth. In adults it is osteomalacia, where existing bone is poorly mineralised, and that one does have a feel to it. Deep aching in the hips, thighs, ribs or lower back, worse on pressure, along with muscle weakness that shows up as difficulty rising from a chair or climbing stairs.

Myth. Tiredness on its own is not a reliable sign of low vitamin D. It is the most common reason people test, and most of the time the test comes back adequate and the tiredness has another cause.

Unsettled. Low mood is the other complaint people bring in, and the trials make a strange picture of it. Across randomised trials vitamin D shifted depression scores by only a small amount, and the shift turned up in people whose blood level was already above 50 nmol/L rather than in the people below it. That is backwards from how a shortage should behave. Five years of 1,600 or 3,200 IU a day in older adults who were not deficient to begin with prevented no new cases of major depression. Something small is moving in those numbers and low vitamin D is not a good explanation for it.

The muscle side needs one qualification too, because it does not behave the way the word deficiency suggests. Active vitamin D analogues given to older people cut falls by about a fifth. The same trials measured grip strength, back extensor strength and overall muscle strength, and none of the three moved. Fewer falls with no stronger muscles means the help is coming from somewhere other than the weakness people picture.

Who is genuinely more likely to be low

People with darker skin living far from the equator, people who cover up or stay indoors, and adults over 65. Also people with a BMI of 30 or more, people after gastric bypass surgery, and anyone with a condition that blocks fat absorption. Winter at high latitude affects everyone, because sunlight strong enough to make vitamin D is not available for several months.

Food is a weak lever here. Few foods naturally carry much vitamin D beyond oily fish and fish liver oils, which is why clinicians check a blood level instead of asking what you eat, and why fortified milk and cereal supply most of what people get.

If the number comes back borderline

Before that number frightens you, know how ordinary it is. About one person in six worldwide sits below 30 nmol/L and nearly half of everyone falls below 50. A low reading is the common case rather than the alarming one.

And the one sign with a measured blood threshold behind it is rickets in children. It starts to appear below about 28 nmol/L in children getting enough calcium, and below about 40 nmol/L in children who are not. Calcium changes where the line sits, which tells you how much a single cut-off on a lab report can carry on its own.

A low result is worth correcting. A borderline one in someone with no symptoms is where the evidence turns unhelpful, and it is better to know that before committing to a daily habit.

Myth. Topping up a level that is already adequate does not buy protection. A meta-analysis of 81 randomised trials in 53,537 people found vitamin D had no effect on total fractures, hip fractures or falls. The Cochrane review of 53 trials in 91,791 people rates as high quality the evidence that vitamin D alone does not prevent hip fracture. Larger doses do not help either. Over three years, 4,000 and 10,000 IU a day left wrist bone density lower than 400 IU a day did.

Two medicines belong on the risk list. Orlistat reduces absorption of vitamin D from food and supplements, and statins, by cutting cholesterol production, may reduce how much vitamin D the body makes from it. Neither is dramatic on its own. Both are worth adding to the reasons to ask for the test rather than to wait for a symptom that may never come.

If the test comes back low, food is the slow lever

Two results set the expectation. Sixty-three adults in Norway ate 750 g of salmon a week for eight weeks through the autumn and their blood vitamin D still fell, less than in people eating cod or no fish, but it fell. Fortified food does move the number: across 34 publications in nearly 4,000 adults and children, an average of 16 micrograms a day from fortified foods raised blood levels by 21 nmol/L, and it raised them more in the people who started below 50. D3 did more than D2.

So a genuinely low result is corrected with a measured dose and a repeat test. A shopping list is the slow version of the same thing, and in the months when you would notice it works least well.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Where to get it from food

• Mackerel, salted — 20.2 µg per 1 piece (5-1/2" x 1-1/2" x 1/2") (101% DV)
• Salmon, sockeye, canned, drained solids — 17.9 µg per 3 oz (89% DV)
• Salmon, sockeye, cooked — 14.2 µg per 3 oz (71% DV)
• Trout, rainbow, farmed, cooked — 13.5 µg per 1 fillet (67% DV)
• Salmon, pink, canned, drained solids — 12 µg per 3 oz (60% DV)

All vitamin D sources ranked →

Full guide: Vitamin D: what supplements do for bones, and what large trials found they do not do