If you value confidentiality of your medical records, I suggest you read these and opt out from the database. You can always opt in at later stage if you decide to opt in.
Form to opt out
IMHO, I do not think likes of think-tank, commercial companies, pharmaceutical companies, health charities
or Universities and other academic organisations do not need to know my medical history. If I am a member and if I think the charity and myself would benefit by revealing my info then I would do so myself.
Where did the maximum 1 mg a day of Hydroxocobalamin come from. 
B12 Deficiency - GP Only Carrying Out Total Serum Test 
Pernicious Anemia treatment
