What should you know about vitamin D and B complex?

Vitamin D helps regulate calcium use, bones and muscle function. B-complex products contain several vitamins involved in energy metabolism, blood-cell production and nerve function. They are not interchangeable, and taking a large combination product does not automatically correct tiredness, low mood or concentration problems.

Fatigue, daytime sleepiness, irritability and difficulty concentrating can have many causes, including poor sleep, stress, anaemia, thyroid problems, medication effects or depression. A symptom alone does not show that a vitamin deficiency is present. Some B vitamins can build up or cause harm at high doses, so the label and your medical history matter.

Review your diet, sun exposure, medicines and health conditions with a clinician or pharmacist before starting a supplement. Testing may be useful when symptoms, restricted eating, digestive disease or another risk factor raises concern. Use the recommended product and dose, and tell the clinician about every supplement you take.

Choose food sources where possible: eggs, dairy or fortified foods, legumes, vegetables, fish and meat can provide different B vitamins, while vitamin D may come from fortified foods and safe sunlight exposure. Do not use supplements as a substitute for assessment of persistent fatigue or mood change.

Arrange a medical review if fatigue, sleepiness, low mood, anxiety, irritability or concentration difficulty persists, interferes with daily life or appears with weight change, numbness, weakness or breathlessness. Seek urgent help for thoughts of self-harm, sudden weakness, confusion or severe breathing difficulty.

Could my symptoms be caused by a vitamin deficiency or another condition? Do I need blood tests? Which ingredients and dose are appropriate with my medicines, diet and health history? How long should I use the supplement before reviewing whether it helps?