[andruby]

My family runs a blood analysis lab in Belgium for which I wrote some of the statistics gathering software.

The thresholds for 25-OH vitamin D: <20 ng/mL → deficient, 20–30 ng/mL → insufficient.

When I looked at all 1738 blood samples that had their Vitamin D tested between Feb 1, 2020 and Mar 13, 2020 (We were looking into the link between Vitamin D and COVID-19): The median (P50) was 20.1 ng/mL and the average was 22.4 ng/mL. Standard deviation: 11.24 ng/mL Half the samples were deficient, and the next 20% was insufficient.

Coming out of winter in Europe in a country with limited sunshine: most of the population is deficient in Vitamin D.

Histogram: https://files.catbox.moe/p785wx.png

[vintermann]

Worth noting all the three big studies mentioned in the article were on Americans.

[strken]

The last of the three was done on Australians. Not that it changes your point, given the latitude of Australia.

[bluenose69]

The curve on your diagram makes me think that you've fitted a normal (Gaussian) curve to the data. By eye, the distribution looks a bit more like log-normal, and so if you're still working on the data, you might want to try that to see. Not that anything you've said or concluded seems wrong, though.

[andruby]

The normal curve in the image is there for operators to visually check if the machine results are normal distributed or not. It's a "stencil", not data.

The software actually does a Lilliefors normality test which returns a big No on this data.

[bluenose69]

Ah, thanks for the information.

[dizhn]

What do you think about the thresholds themselves? How often are they updated usually with new research?

[seba_dos1]

Based on what I've seen while researching the topic for my own health purposes: the thresholds differ in various sources, but in general research appears to suggest that they may tend to err on the too low side rather than too high (there's quite a lot of headroom between what's often considered excessive and what's actually known to be toxic, while the lower end is much fuzzier).

[andruby]

I'm an engineer, not a clinical biologist or researcher. I have no idea.

On a personal level: I used to struggle with "winter dip". Taking Vitamin D supplements, as well as moving to South Africa, has both improved it a lot