Vitamin D Deficiency: Signs and Safe Sunlight

What does vitamin D actually do?

According to the NHS, vitamin D helps regulate calcium and phosphate in the body, and those minerals keep bones, teeth and muscles healthy. The NIH Office of Dietary Supplements adds that vitamin D lets your body absorb calcium, that muscles need it to move, and that nerves need it to carry messages between the brain and the body.

What happens if you do not get enough?

In children, a lack of vitamin D causes rickets, in which bones become soft, weak, deformed and painful. In teenagers and adults it causes osteomalacia, which shows up as bone pain and muscle weakness. Both sources also note that bones become fragile and break more easily.

These signs are vague and easy to blame on something else, which is why guessing is a poor approach. Ongoing bone or muscle pain deserves a proper assessment.

Who is most likely to be short of vitamin D?

The NIH lists these groups as being at higher risk:

• Breastfed infants, because breast milk alone does not supply enough
• Older adults, whose skin makes less vitamin D from sunlight
• People who get little sun exposure
• People with darker skin, who make less from the same amount of sun
• People with conditions that affect fat absorption, such as Crohn's disease or celiac disease
• People with obesity, or who have had gastric bypass surgery

The NHS similarly singles out people who are housebound, people in institutions, and people with dark skin as needing to think about vitamin D all year.

Where does vitamin D come from?

Your skin makes vitamin D from sunlight, and it is in a small number of foods. The NHS lists oily fish such as salmon, sardines and mackerel, red meat, liver, egg yolks, and fortified foods such as some spreads and cereals. The NIH adds fortified milk, at about 3 micrograms per cup, plus fortified plant-based milks.

How much sunlight is sensible?

Honest answer: there is no single number that fits everyone. How much sun you need varies with skin tone, age, time of day and season, and official sun-exposure guidance is written for particular countries. What both sources agree on is that too little sun exposure is a real cause of deficiency. Getting some daylight in the course of your day is sensible; burning your skin is not.

How much vitamin D do you need?

Official recommendations differ slightly between countries, which is worth knowing before you compare labels:

• The NHS recommends 10 micrograms a day for adults and children aged 1 and over, and 8.5 to 10 micrograms for babies under 1.
• The NIH recommends 15 micrograms (600 IU) a day for ages 1 to 70, 20 micrograms (800 IU) for adults over 70, and 10 micrograms (400 IU) for infants under 1.

There are also upper limits. The NHS says adults and children over 11 should not take more than 100 micrograms (4,000 IU) a day, children aged 1 to 10 no more than 50 micrograms, and infants under 12 months no more than 25 micrograms.

Can you take too much?

Yes. The NIH warns that too much vitamin D can cause nausea, vomiting, muscle weakness, kidney stones and, at extreme levels, kidney failure. High-dose vitamin D is not harmless, and this is the main reason not to start a supplement on your own guesswork.

When to see a doctor

Ask your doctor about a blood test, and follow the advice you are given, rather than choosing a dose yourself. See a doctor if:

• You have ongoing bone pain, or aching in the hips, back, legs or ribs
• You have muscle weakness, difficulty climbing stairs, or getting up from a chair
• You have broken a bone after a minor fall
• Your child has bowed or bent legs, delayed walking, or pain on weight-bearing
• You are in one of the higher-risk groups above and have never been tested
• You have taken high-dose vitamin D and feel nauseated, are vomiting, or feel very weak

For severe vomiting with confusion or a suspected broken bone, call Rescue 1122 where available, or go to the nearest hospital emergency department.