Vitamin B12 deficiency living in infants

Overview

Vitamin B12 deficiency in infants means the baby does not have enough vitamin B12. Vitamin B12 is important for making red blood cells and keeping the nervous system healthy.

It is rare in developed countries, but it can happen more often in babies whose mothers are vegan, have pernicious anemia, or have had weight loss surgery.

It primarily affects infants, especially those who are exclusively breastfed by mothers with low vitamin B12 levels.

Symptoms

Common symptoms

• Lack of energy (lethargy)
• Poor feeding or difficulty sucking
• Irritability or fussiness
• Failure to gain weight or grow as expected
• Pale skin

Symptoms in children

• Developmental delays (e.g., not sitting, crawling, or talking on time)
• Weakness or floppiness
• Difficulty walking or unsteady movements
• Changes in behavior, such as being withdrawn or clingy

Symptoms in older adults

• Vitamin B12 deficiency in older adults is usually due to poor absorption, but symptoms are different from those in infants. This article focuses on infants.

Causes

Main causes

• The mother has low vitamin B12 during pregnancy or while breastfeeding – common in vegan or vegetarian diets without supplements.
• The mother has a condition called pernicious anemia, where the body cannot absorb B12 from food.
• Rarely, the baby has a problem absorbing B12 from the start.

Risk factors

• Mothers who follow a strict vegan or vegetarian diet without B12 supplements
• Mothers with a history of weight loss surgery (gastric bypass or sleeve)
• Mothers with celiac disease, Crohn's disease, or other gut conditions that affect absorption

When to see a doctor

See a doctor urgently if:

• If your baby is very sleepy, difficult to wake, or not feeding at all.
• If your baby has a seizure or stops breathing for a moment.

Book a routine appointment if:

• If you notice your baby is not gaining weight as expected.
• If your baby seems unusually tired, irritable, or is not reaching developmental milestones around the expected age.

Diagnosis

A doctor will ask about the mother's diet and the baby's symptoms. They will then order blood tests to measure vitamin B12 levels and look for signs of anemia.

Tests that may be done

• Blood test for vitamin B12 level
• Complete blood count (CBC) to check for anemia
• Methylmalonic acid (MMA) test – a more sensitive marker of B12 deficiency
• Homocysteine level – often elevated in B12 deficiency

What to expect at your appointment

The blood test is quick – a small amount of blood is taken from the baby's heel or vein. Results usually come back within a few days. If the test shows low B12, the doctor will explain the next steps, which may include treatment right away.

Treatment

The main treatment is giving extra vitamin B12 to the baby. This helps correct the deficiency and allows normal development to continue.

Self-care at home

• If you are breastfeeding, your doctor may advise you to take a vitamin B12 supplement to improve your own levels, which will help your baby through breast milk.
• For older babies who have started solid foods, include B12-rich foods like eggs, dairy, or B12-fortified cereals (after checking with your doctor).

Medical treatments

The doctor will prescribe vitamin B12 injections or high-dose oral drops for the baby. The dose and how often it is given depends on how low the levels are. Treatment usually starts immediately after diagnosis. The baby will be monitored with repeat blood tests until levels are normal.

When is surgery considered?

Surgery is not needed for vitamin B12 deficiency.

Living with this condition

Once treatment begins, most babies improve quickly. You will need to attend follow-up appointments to check blood levels and monitor development. Keep a record of your baby's feeding, growth, and milestones.

Lifestyle tips

• Make sure you (if breastfeeding) are eating a balanced diet or taking B12 supplements as recommended.
• Attend all scheduled check-ups and blood tests.
• Talk to your health visitor or pediatrician about any new symptoms or concerns.

Diet and exercise

For babies, the main focus is on adequate B12 through treatment or diet. As your baby grows, introduce age-appropriate B12-containing foods. Exercise is not a concern for infants, but encouraging tummy time and play helps development.

Mental health and emotional wellbeing

Caring for a baby with a health condition can be stressful. It is normal to feel worried. Reach out to family, friends, or a support group. Your doctor can also suggest counselling services if needed.

Prevention

Yes, in many cases. Mothers can prevent deficiency by eating a diet rich in B12 or taking supplements during pregnancy and while breastfeeding. If you have a condition that affects absorption, talk to your doctor before or during pregnancy.

Vaccines

There are no vaccines for vitamin B12 deficiency.

Screening programmes

Routine screening is not done for all babies. However, if you are at high risk (e.g., vegan diet, gut condition), your doctor may recommend checking your B12 levels during pregnancy and your baby's levels after birth.

Complications

If left untreated

• Delayed development – baby may be slow to sit, crawl, or walk
• Anemia – low red blood cells causing pale skin and tiredness
• Nerve damage – can lead to permanent weakness or coordination problems
• Growth problems – failure to thrive and gain weight

Long-term outlook

With early diagnosis and proper treatment, the outlook is excellent. Most babies catch up in growth and development. Even if there are some delays, treatment can stop them from getting worse. Regular follow-up helps ensure your baby stays on track.

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