If your vitamin D levels are low, what’s a useful starting dose?

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I was talking with someone yesterday about his vitamin D levels. He had these tested recently and found these came in at 15 ng/ml (about 38 nmol/l). Personally, I like vitamin D levels to be maintained in the region of 50 ng/ml. So, I suggested he take 5,000 IU of vitamin D3 for three months after which he’ll re-check his levels.

He asked me how I arrived at a dose of 5,000 IU. Good question. This ‘starting dose’ is actually based on my experience. It’s this sort of level of intake that I find can get vitamin D levels up from quite low levels to more optimal levels in a reasonable amount of time (say, a couple of months).

When I started supplementing myself with vitamin D (starting levels, 15 ng/ml), I thought I was being gung-ho by taking 2,000 IU a day. I soon realised this was an inadequate dose for my requirements. I now take about 5,000 IU during the summer and about 7,500 IU per day during the rest of the year.

Later in the day, I decided to see if there was any recent science in this area. I found a study published just a few days ago in which individuals with vitamin D deficiency were treated with either 2,000 or 5,000 IU vitamin D for 3 months [1]. All individuals started with vitamin D levels at or below 20 ng/ml.

At the end of the study, those taking 2,000 IU saw their vitamin D levels increase by about 80 per cent, while those on 5,000 IU had their levels more than treble on average. At the end, 45 per cent taking 2,000 IU had achieved levels of 30 ng/ml or more, compared to 93 per cent taking 5,000 IU.

No-one in the study suffered from adverse symptoms or raised blood levels of calcium (a theoretical risk of high vitamin D levels).

This study appears to provide some support for the idea that those with low vitamin D levels might start with a dose in the order of 5,000 IU. How people respond to supplementation is, however, quite variable, which is why I advise monitoring blood vitamin D levels.

Previously I have used testing provided by Grass Roots for Health and Vitamin D3 World. However, here in the UK, I’ve recently started to use this service out of City Hospital in Birmingham which seems to be very good (and economical). See here.


1. Diamond T, et al. Effect of oral cholecalciferol 2,000 versus 5,000 IU on serum vitamin D, PTH, bone and muscle strength in patients with vitamin D deficiency. Osteoporos Int. 2012 Mar 16. [Epub ahead of print]

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