"Vitamin D and cancer mini-symposium: the risk of additional vitamin D."
this paper by Vieth R explains that in practice it has been shown intakes of below 10,000iu/daily for adults are absolutely safe.
"Evidence from clinical trials shows, with a wide margin of confidence, that a prolonged intake of 10,000 IU/d of vitamin D(3) poses no risk of adverse effects for adults, even if this is added to a rather high physiologic background level of vitamin D."
It generally takes prolonged (many months) intake of more than 40,000iu/daily before levels above 150ng/mL are reached and the possibility of adverse events is significant. Indeed it may be that 200ng is the level where adverse events are recorded.
However, most readers here can take comfort from the fact that Dr Davis of the Heartscanblog has shown in his Wisconsin Practice for Heart Patients that intakes of 5000iu usually are sufficient for most of his female patients and 6000iu for males. However, he does point out that there is a huge variation in the efficiency at which we absorb and use D3 so regular 25(OH)D testing is a good idea to confirm you are always in the region of 55ng 137.5nmol/l at which human breast milk flows replete with D3, peak muscle performance is achievable and is the level associated with the least incidence of chronic conditions such as Diabetes, cancer, heart disease, MS,
Grassrootshealth D Action Campaign
Grassrootshealth are a charity promoting knowledge of the latest Vitamin D3 research. As part of their work they are running a trial monitoring 25(OH)D status against hospital interventions.
If you participate in this trial you can have your 25(OH)D checked up to twice yearly for $40 a time, roughly £24. It's a simple finger prick, 2 drops of blood on a test strip that you return in the post and they send you a link to your results.
Because of the difficulty in getting optimal amounts of vitamin D from sun exposure and adequate amounts from diet it's really worth participating in this trial.
When buying vitamin D3 you may want to consider the form Vitamin D3 Plus suggested by Dr Cannell of the Vitamin D Council
However, I've always found the standard vitamin D3 capsules Biotech Pharmacal produce are fine for me. When buying from Bio Tech if your order is likely to cost more than £18 to the UK it may be worth phoning your order through as you can then ask for the customs label declaration to state the wholesale rather than retail value, to avoid the excessive £8 UK Post Office handling fee for collecting the £3 customs duty.
As Vitamin D3 supplementation is a long term commitment it is worth using the cheapest source. I find these Now Foods, Vitamin D-3, Highest Potency, 5,000 IU, 120 Softgels absolutely fine.
The postage IHERB charge is generally less than elsewhere and by using the Rewards code WAB666 you can save $5 and by spreading the rewards code you will be given when you have ordered you can get further discounts from subsequent orders.