Wow, my Vit D is low

Despite taking 4,000 to 8,000 units per day for the past few months.

National Institute for Health and Care Excellence

NICE

Do not routinely test for vitamin D deficiency in people who are asymptomatic.

https://cks.nice.org.uk/topics/vitamin-d-deficiency-in-adults/diagnosis/diagnosis/

Check the vitamin D level by measuring serum 25-hydroxyvitamin D (25[OH]D) if a person has:

Musculoskeletal symptoms

Suspected osteomalacia.

Chronic widespread pain with other features of osteomalacia (such as proximal muscle weakness).

Suspected bone disease that may be improved with vitamin D treatment, such as osteomalacia or osteoporosis.

Known bone disease, where correction of vitamin D deficiency is needed prior to specific treatment, such as:

Prior to Paget’s disease treatment with a bisphosphonate.

Note: asymptomatic people at higher risk of vitamin D deficiency do not need routine testing for vitamin D deficiency,

but should be advised on the need for maintenance dose vitamin D supplementation.

Source