Optimum Vitamin D Level

Most people would agree that the vitamin D blood level which gives best protection from disease, and lowest mortality rates, would be the best target to aim for – the optimum level.

But this value will need to be determined by many human studies. Until that has been completed, there will be different opinions as to the best vitamin D level to aim for.

But as hundreds of vitamin D trials have already been conducted, there is enough information already to define some useful bands or ranges:

These ranges are not universally accepted — some medical authorities still recommend 25(OH)D levels as low as 20 ng/ml, which is 50 nmol/L.

Here are the main reasons why we recommend 25(OH)D blood levels of 50-65 ng/ml

1. People whose vitamin D levels are above 40 ng/ml are much less susceptible to a wide range of major and minor diseases than are people with deficient vitamin D levels, according to several medical and scientific studies. This continuous increase in benefits does not fizzle out at 40 ng/ml.
2. For many diseases (e.g. breast cancer, several other cancers, type 1 diabetes and multiple sclerosis) the improvement in disease incidence continues until vitamin D levels reach 50 ng/ml or higher. See chart Disease Incidence by Serum 25(OH)D.
3. Many people who spend their days in sunlight (farmers, builders, hunters, field-workers, fishermen etc.) naturally maintain vitamin D blood levels of 50 to 80 ng/ml, without any supplementation. (Most of mankind and his ancestors have lived this way, naturally.) See Dr Heaney’s paper “Vitamin D in Health and Disease”.

Among the hundreds of vitamin D studies, there have been at least two that seemed to show that the benefits of vitamin D taper off at some point, and then gradually decline at still higher vitamin D levels. These studies have suggested that the optimum level might be as low as 36 to 45 ng/ml. But in both cases, the evidence for negative benefit above these levels is slim. See this analysis by Professor John Eisman.

There are other studies that show vitamin D benefits increasing well beyond these levels.

As we do not yet have all the facts, we must weigh up the evidence from all sources. Our conclusion is that, for people in good health, 50 – 65 ng/ml provides maximum benefits, as long as the vitamin D co-factors are also in their appropriate ranges.

Vitamin D Co-factors

The main vitamin D co-factors are calcium, magnesium and vitamin K2.

Here is a quick example of why co-factors are important. When your body converts Vitamin D — from cholecalciferol into calcidiol and then into calcitriol — it uses up magnesium. So if you increase your vitamin D level without taking enough magnesium, you could start to notice symptoms of magnesium deficiency.

For more information, see Vitamin D Co-factors.

To find out your current vitamin D blood level, the best way is to have it tested by a pathology lab. See Vitamin D Testing. If you don’t wish to have it tested, you can estimate it.