Ok, I get it.

Now let me turn to what might be a more practical problem. What if, for some reason, you cant get a 25 Hydroxy D test done ? Say your doctor wont prescribe it or the labs wont do it or its too expensive ... or some such thing.

In that case, is it still safe to supplement at 5K IU and more per day ? What would be a meaningful but "safe" dosage in such a case ?

Grassrootshealth D Action do them at cost price and post worldwide, however there are some places in the USA (New York is one) where they consider the adults there are too immature and irresponsible to take full responsibility for their own health.

A total intake of around 1000iu for each 25lbs you weight is probably about right, however if you have a chronic health condition that involves inflammation then your body will be using up the anti inflammatory vitamin D3 faster than other peoples. So more may well be required. If you have Celiac or Diabetes or are obese then you need a 25(OH)D test to check to see if you are taking sufficient to keep you level such that you have a reserve of vitamin D3 stored so you always have a reasonable level available for circulating as Calcidiol.

We can see from the research that below concentrations of 100nmol/l 40ng/ml it doesn't have much effect on cancer cells but at higher concentrations it does. This is why some of the "potentially cancerous" breast cells they see on mammographies disappear come the summer and higher circulating calcidiol levels.

Getting and staying above 55ng/ml 137.5nmol/l is associated with less chronic illness because at that level we always have some working capital (circulating calcidiol) to deal with pathogens, inflammation, cancer if it occurs.

Living in India you should be able to have access to sunshine.
However urban pollution may be a problem as maybe exposing skin to sunlight is culturally unacceptable.

However, as I've pointed out there is much we still have to learn about this vitamin and UVB exposure raises not only vitamin D3 and 25(OH)D but also other substances the role of which has not yet been fully researched. There could well be other forms such as 24,25(OH)2D3 which we thought were inactive but have roles that we simply haven't discovered as yet.

So I'm happy if people take 5000iu/daily/D3 and get short sessions of nonburning UVB containing sun on as much skin as possible, then cover up. (to protect the newly made vitamin d3) Unless you are closely monitoring your 25(OH)D level I don't think it's a good idea to take more than 10,000iu/daily and get sun exposure for long periods though I do think some people with chronic conditions will require somewhat more than 10,000iu/daily to get on top of the inflammation.

But regular testing allows you to see how your body is responding to the regime you've chosen.

Ok, thats very clear. Thanks.
So 1000 Iu per 25 pounds is ok even without a blood test ? For how long ?

Also, in hyperlipid's blog, he says there should not be too much variation in Vitamin D intake. So doing 2000 IU per day summer and 5000 IU per day in winter is not OK, right ?

FOR EVER.

WRONG. Ideally you need to keep your level HIGH and STABLE.

DAILY use of D3 plus sun exposure is the best way to guarantee a high stable 25(OH)D ideally above 55ng/ml and best about 60ng/ml But if you have cancer then go as high as you can ideally around 80ng/ml would be best. The higher the circulating 25(OH)D the more able it is to stop proliferation of cancer cells.

In the paper Petro (Hyperlipid) is discussing Vieth explains how it may be that the Finnish problem of those with higher vitamin D having more aggressive prostate cancer may occur. Remember Finland is FAR FAR NORTH. People with a high vitamin D status in Finland may suffer, by taking winter sun breaks, getting loads of sun exposure in summer and absolutely none in Winter, huge variation in 25(OH)D status. This change in status causes disruption in the fine tuning of the immune system that we need to avoid.

So in winter it is better to increase your vitamin D status and then reduce intake just slightly in the summer if you are going outside and exposing a reasonable amount of skin to sunshine.

It is impossible for me (or anyone else) to guess how any other particular individual responds to supplemental/dietary/sun sources of vitamin D3 so the only way is a test from time to time. That way you know how your body is responding to that amount of sun/supplement/dietary Vitamin d. But remember Vieth has shown that up to 10,000iu/daily is safe even in sunny countries and it is better to be on the high side than the low side.

At latitude 52 I think 5000iu/d in summer and 7000iu/daily in winter should be the minimum to ensure levels stay around 60ng/ml.
It's only at higher levels that the anti cancer proliferation power of 25(OH)D is effective so the longer your levels are kept above 60ng/ml the better.

Those lucky people who have got a winter sun holiday booked on a tropical island can raise their 25(OH)D status over the weeks BEFORE they depart, abstain from supplements while they are sunning on the beach, and restart supplements on the flight home and continue with effective strength D3 after they get back home.
That way the immune system should have time to become accustomed to higher levels before the flight out and the decline after the return home will be slower and the change in status requiring less adjustment.