I'll talk to my GP about taking 10,000.
That figure is measured in IU = international units
Today, many countries still use the IU to measure vitamin D; 1 IU of vitamin D is equivalent to 0.025 micrograms (abbreviated as either mcg or μg) of cholecalciferol or ergocalciferol. Conversely, 1 microgram of vitamin D equals 40 IU of vitamin D.
10,000 IU = 250 micrograms.
The recommended daily safe upper limit for Vitamin D in the UK is 4,000IU = 100 micrograms.
Taking too much can be harmful.
Always get your levels checked and get medical advice before taking more than the recommended allowances.