Vitamin D2 and D3

[Guest guest]

> Is it your impression there is something wrong with the D3 version

of vitamin D?

>

> Rodney.

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Rodney,

Vitamin D3, or cholecalciferol, what you're taking, should be fine.

Vitamin D2 is ergocalciferol. Docs in the US prescribe D2 because

that's the version that's available by prescription. D2 is a

plant-based sterol. Its hydroxylated derivatives are probably

slightly less effective than the hydroxylated derivatives of vitamin

D3, which is the compound made when you go out in the sun in humans.

vitamin D3 (cholecalciferol) per se is not believed to have much

activity, although who knows? It is first 25-hydroxylated in the

liver, and then 1-hydroxylated in the kidneys. The active compound is

calcitriol - 1,25 dihydroxy-D3. Recent evidence suggest that tissues

other than the kidneys contain the 1-hydroxylase, and so the 25-OH-D

may of itself be biologically active due to local within-cell

1-hydroxylation and activation.

There's a great debate going on know as to how much D is enough / too

much. The current RDA is, I believe 200-400 IU. There are a number

of papers out there suggesting that 800 IU is required to help

osteoporosis, and that 1000 IU per day may be required for D to help

prevent cancer. (Vitamin D3 inhibits division of prostate cancer

cells, for example). The amount of D required depends on how much sun

exposure one gets - someone not exposed to the sun at all may need

more than someone who gets out a bit, and there is no reason to give

vitamin D who get out in the sun on a regular basis. There have been

reports of nursing home patients who can't get up from a sitting

position, confined to wheelchairs, and this turned out to be from

Vitamin D deficiency myopathy- which reversed on giving vitamin D.

The " minimum dose to cause potential harm " for Vitamin D has been

officially set at 2000 IU per day, although some have argued that this

is too low, given that exposure to sunlight gives higher equivalent

serum levels of 25-hydroxy-D. Reinhold Vieth from Toronto has been

championing this approach. This is why a factor of 5 (2000/400) has

been used to set the upper recommended limit at 400 IU per day, though

this is being re-examined, as I understand it. Vieth points out that

there are only a few papers that point to any problem with vitamin D

in the 2000 IU per day range, and these showed a slight increase in

serum calcium or urinary calcium. Vieth points to other papers that

suggest that a 2000 IU daily dose is fine or even a bit low.

Here are some of Vieth's papers:

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=16019727 & query_hl=12 & itool=pubmed_docsum

Vieth R.

The role of vitamin D in the prevention of osteoporosis.

Ann Med. 2005;37(4):278-85. Review

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=15776217 & query_hl=12 & itool=pubmed_docsum

Dawson- B, Heaney RP, Holick MF, Lips P, Meunier PJ, Vieth R.

Estimates of optimal vitamin D status.

Osteoporos Int. 2005 Jul;16(7):713-6.

Woo TC, Choo R, son M, Chander S, Vieth R.

Pilot study: potential role of vitamin D (Cholecalciferol) in patients

with PSA relapse after definitive therapy.

Nutr Cancer. 2005;51(1):32-6.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=15260882 & query_hl=12 & itool=pubmed_docsum

Vieth R, Kimball S, Hu A, Walfish PG.

Randomized comparison of the effects of the vitamin D3 adequate intake

versus 100 mcg (4000 IU) per day on biochemical responses and the

wellbeing of patients.

Nutr J. 2004 Jul 19;3:8.

Personally, I am wary of taking greater than 800 IU of vitamin D per

day, and I also limit my calcium supplements to 500-800 mg/day.

Vieth's point of view is not yet widely accepted, but things seem to

be changing to move the RDA up to the range of 800 IU per day.

Risks of too much vitamin D:

Too much D can give rise to hypercalcemia, vascular calcification and

kidney failure. Most of the papers where this happened were due to

self-medication or other dosing errors using enormous (tens of

thousands of IU) amounts of ergocalciferol or cholecalcifero. One

case happened when a dairy added way too much vitamin D to milk

products. I don't know of any reports of anyone getting into trouble

with daily vitamin D doses in the range of 1-2000 IU per day, but this

is not really my area of research. Also, vitamin D may increase the

risk of developing milk-alkali syndrome.

Milk-alkali syndrome:

One potential related problem, not directly related to vitamin D, but

which might be exacerbated, at least theoretically, by vitamin D, is

the interaction of alkalosis with vascular calcification. The

syndrome of milk-alkali was initially found in people self-treating

with alkali and milk to treat ulcers. It now is being found in people

taking larger amounts of calcium supplements and some type of

bicarbonate therapy, even without milk products. Some studies suggest

that milk-alkali therapy might be exacerbated by taking vitamin D

along with calcium supplements but this has not been well worked out.

As more foods become fortified with vitamin D (orange juice, bread,

cereals) people are worried that milk-alkali syndrome may become an

increasing problem.

There are one or two reports of milk-alkali in people taking as little

as 1-2 g/day of calcium supplements. Since the regulatory gurus are

recommending up to 1.5 g/day total calcium intake in women, this is

getting close to ranges where problems have been reported. Most of

the people who had problems with milk-alkali syndrome are believed to

have had reduced kidney function to begin with. The risk in people

with normal kidney function is not well known.

Milk-alkali is no joke - it often presents as kidney failure requiring

dialysis.

There are almost no data about milk-alkali in people taking

non-standard diets, esp. alkalinizing diets, such as those containing

very low protein, or composed mostly of alkalinizing foods.

High-bicarbonate mineral water may be a problem, theoretically - most

such water is fine, but some mineral waters have quite high levels of

alkali (sodium bicarbonate). So someone drinking a lot of high-bicarb

mineral water, taking a lot of yogurt, and also taking calcium

supplements may be the equivalent of the ulcer patient from years gone

by sipping antacids and milk.

The acid in the normal diet comes mainly from protein. I am

interested in reading the recent books recommending alkalinization of

the diet. Theoretically, such diets have an increased risk of

milk-alkali, especially if calcium supplements or a lot of milk are

consumed.

So, like anything else in medicine, amounts are critical, and

individual susceptibility is also an issue.