Low vitamin d (25-oh)

Written to our editorial standards · reviewed against published research· Updated 2 Jun 2026

Low vitamin D is extremely common, especially in winter and in people who spend most of the day indoors, and is linked to low mood, muscle weakness, fatigue, and more frequent infections.

Vitamin D is made in the skin from sunlight, so levels fall in the darker months and in those with limited sun exposure or darker skin. It has receptors throughout the body, which is why a shortfall is associated with low mood, achy weak muscles, and weaker immunity. It is cheap to test and easy to correct.

Common causes

  • Limited sun exposure or indoor lifestyle
  • Darker skin tone
  • Winter at higher latitudes
  • Older age
  • Obesity or malabsorption

Associated symptoms

  • Low mood, worse in winter
  • Muscle aches or weakness
  • Fatigue
  • Frequent colds or infections
  • Bone or back aches

Nutrients that can help

Vitamin D3 + K2
See the guide →
What to do

Take vitamin D3 with vitamin K2 and a meal containing fat. The dose depends on how low you are, so retest after about 3 months and adjust. Sensible sun exposure helps in summer.

When to see a doctor

Very low levels or symptoms of bone pain warrant a doctor's review, and high-dose vitamin D should be monitored with testing to avoid going too high.

Full marker
Vitamin D (25-OH): ranges, what it measures & both directions
Read the Vitamin D (25-OH) guide →

Common questions

What does low vitamin d mean?
Low vitamin D is extremely common, especially in winter and in people who spend most of the day indoors, and is linked to low mood, muscle weakness, fatigue, and more frequent infections. Vitamin D is made in the skin from sunlight, so levels fall in the darker months and in those with limited sun exposure or darker skin. It has receptors throughout the body, which is why a shortfall is associated with low mood, achy weak muscles, and weaker immunity. It is cheap to test and easy to correct.
What causes low vitamin d (25-oh)?
Limited sun exposure or indoor lifestyle; Darker skin tone; Winter at higher latitudes; Older age; Obesity or malabsorption.
How do I raise my vitamin d (25-oh)?
Take vitamin D3 with vitamin K2 and a meal containing fat. The dose depends on how low you are, so retest after about 3 months and adjust. Sensible sun exposure helps in summer.
When should I see a doctor?
Very low levels or symptoms of bone pain warrant a doctor's review, and high-dose vitamin D should be monitored with testing to avoid going too high.

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Educational use only, not medical advice or diagnosis. Reference ranges vary by lab, age, sex, and medication, and a single result is read in context. Always review your results with a qualified clinician.