Child Low Vitamin D: What Does It Mean and What Happens Next?

Low vitamin D in a child means a blood test or the doctor's assessment suggests the child is not getting or making enough vitamin D. Vitamin D helps the body control calcium and phosphate, which growing bones need. A low result is common and often found before any symptoms, but it needs a plan from your child's doctor.

The skin makes vitamin D from sunlight, and some comes from food. When levels stay low during growth, bones can become soft and weak. In children this is called rickets. Healthdirect notes that most children with low vitamin D alone do not develop rickets, so a low result is a reason for follow-up rather than alarm.

This guide is for parents and carers reading a child's result or worried about signs. It cannot interpret your child's specific number. For how the 25-hydroxy vitamin D test works and how labs label results, see the separate guide on low vitamin D results.

Very low vitamin D can lead to low calcium. Healthdirect says babies and children with low calcium may have muscle cramps or seizures, and that children with very low calcium need hospital treatment. A fit is an emergency.

The NHS advises calling 999 (or your local emergency number) if a child:

• has a fit for the first time or cannot stop shaking;
• has difficulty breathing, grunting, breathing very fast, or the tummy sucking in under the ribs;
• is drowsy and hard to wake, or not responding like they normally do;
• has blue, grey, very pale or blotchy skin;
• has a rash that does not fade when you press a glass against it;
• is not interested in feeding or normal activities, or is extremely agitated or confused.

Rickets develops slowly, so signs are often noticed over weeks or months. The NHS and Healthdirect list signs such as:

• bowed legs, with a large gap between the knees when standing with feet together, or knock-knees;
• swollen, sore wrists, knees or ankles;
• pain in the back, ribs, pelvis or legs, or not wanting to walk;
• weak muscles, cramps or twitching;
• delayed crawling or walking, or being shorter than expected for age;
• late teeth or weak tooth enamel, and in babies a soft spot on the head that is slow to close;
• bones that break more easily.

Healthdirect advises taking a child to a doctor as soon as possible if they have any rickets symptoms, or if you are concerned about their development. MedlinePlus also advises contacting your child's health care provider if you notice symptoms. Do not wait for a routine appointment if signs are getting worse.

To check for rickets, doctors may use blood tests for vitamin D, calcium, phosphate, alkaline phosphatase and kidney function, sometimes with parathyroid hormone. X-rays can show how the growing ends of bones look. Children's normal ranges for many of these tests differ by age and by laboratory, so ask how your child's results compare with the range used by that lab rather than an adult range.

Official sources describe several groups at higher risk. These are reasons to ask about prevention, not proof that a child has a problem.

• babies who are exclusively breastfed, because breast milk contains little vitamin D;
• children with brown or black skin, who need more sunlight to make the same amount of vitamin D;
• children who spend little time outdoors, cover most of their skin, or live where winter sunlight is weak;
• diets low in calcium or vitamin D, including avoiding dairy without a planned alternative;
• babies who breastfeed for a long time without starting solid foods at around 4 to 6 months;
• conditions that affect fat absorption, the liver or the kidneys, and rare inherited forms of rickets.

Sunlight is the main source. The NHS says that in the UK most people can make the vitamin D they need from sunlight between late March or early April and the end of September, but not between October and early March. Children with brown or black skin may need more time outdoors. Protect children from strong midday sun and sunburn, and follow sun-safety advice for babies.

Food helps but rarely provides enough on its own. NHS food sources include oily fish such as salmon, sardines and mackerel, egg yolks, red meat and fortified foods such as some breakfast cereals and fat spreads. A varied diet with calcium-rich foods also supports bones.

Follow your child's doctor and your national health service. In the UK, the NHS states that babies from birth to 1 year who are breastfed, or who have less than 500ml of infant formula a day, "should have a daily supplement containing 8.5 to 10 micrograms of vitamin D throughout the year." It also states that "Children aged 1 to 4 years old should be given a daily supplement containing 10 micrograms of vitamin D." Babies having more than 500ml of formula a day should not be given an extra vitamin D supplement, because formula already contains it.

These are prevention recommendations for healthy children, not treatment for a low result. If your child has a low level or rickets, the doctor will decide on treatment. Other countries may give different advice.

The NHS warns parents to be careful not to give two supplements at the same time, and not to give cod liver oil alongside vitamin drops because it also contains vitamins A and D. Too much vitamin D over a long time can raise calcium levels and harm the bones, kidneys and heart. Ask a pharmacist or health visitor which product suits your child, and check every product's label.

Writing questions down before the appointment can help you leave with a clear plan.

• Is my child's level low for their age, and which range did the lab use?
• Are there any signs of rickets, and were calcium, phosphate or alkaline phosphatase checked?
• Is this low result likely to be about sunlight and diet, or could another condition be involved?
• What treatment do you recommend, for how long, and how will we know it is working?
• Is a repeat blood test needed, and when?
• Should brothers, sisters or a breastfeeding parent also think about vitamin D?
• Which symptoms mean I should come back sooner?

On SameCase, parents can read de-identified cases from other families and see how verified doctors discussed similar results. Comparing what was asked and which tests were mentioned can help you prepare your own questions. Another child's case cannot tell you what your child has or what treatment is right; that decision belongs to your child's own doctor.