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Vitamin D levels in children around the world

Posted on: June 13, 2013   by  tom.weishaar@gmail.com


In the last year there have been a number of studies looking at vitamin D levels in children in various locations around the world. In this blog I’m going to compare and contrast their results. I’ve created a series of graphs that look like this:Blog-Graphic-1

All of the graphs have three bars. The first bar in each graph is the percentage of the children who have serum 25(OH)D levels below 20 ng/ml (50 nmol/L). There is broad scientific agreement that levels below 20 ng/ml are inadequate for bone health – even the US Institute of Medicine’s Dietary guidelines for vitamin D agree with this.

The second bar in each graph is the percentage of children with levels between 20 and 30 ng/ml (50 – 75 nmol/L). In his highly respected and frequently cited article in the New England Journal of Medicine, Vitamin D deficiency, Michael Holick suggested that this level indicates insufficiency of vitamin D, although other experts will say only that optimum levels for functions of vitamin D beyond bone health are unknown.

The third bar in each graph shows the percentage of children with levels above 30 ng/ml (75 nmol/L).  Holick called this level sufficient, although many others, including the Vitamin D Council itself, think the best current estimate of an optimal population level would be about 45 ng/ml (115 nmol/L).

In some of the graphs, for example, the second one in Figure 1, there is a dark blue area at the bottom of the first and third bars. On the first bar, this represents the percentage of children below 10 ng/ml (25 nmol/L) and on the third bar it represents the percentage of children above 40 ng/ml (100 nmol/L). If these dark areas do not appear in a particular graph, it typically means the study didn’t report these levels, not that the actual percentage for these levels is zero. The title of each graph gives the location and age of the children. If the location was a specific city rather than a nationally-representative estimate, the latitude is included in the title. Finally, the number of children whose data was used to create the estimates is given after “n=” and the mean of the group is given after “m=”.

In Figure 1, the data for Mexico come from Serum 25-hydroxyvitamin D levels among Mexican children ages 2 y to 12 y: a national survey. The Vitamin D Council’s Kate Saley has also written about this study. I calculated the percentages for the U.S. graphs myself, using data from the National Health and Nutrition Examination Survey. The Canadian data come from Vitamin D status in Montreal preschoolers is satisfactory despite low vitamin D intake. The Swedish data come from Serum 25-hydroxyvitamin D levels in preschool-age children in northern Sweden are inadequate after summer and diminish further during winter.

In Figure 1, the group with the best vitamin D levels is, surprisingly, the kids in Montreal. Montreal has the lowest percentage of kids with vitamin D levels under 20 ng/ml and the highest percentage above 30. The Montreal study reported a median for the entire group of 29.8 but did not report a mean. The children in the study were recruited from licensed daycare centers.

Looking at the runners-up, a larger percentage of the children in Mexico are above 30 compared to the U.S., which is good, but a larger percentage is also below 20, which is bad. The children in Mexico have a higher mean. Unsurprisingly, the children at latitude 63 degrees in the far north of Sweden have the largest percentage in this set of graphs below 20, the smallest percentage above 30, and the lowest mean.

It’s difficult to understand what’s going on in Montreal, but we should all have what they’re having. In the U.S., skin color is the most important determinant of vitamin D status, but the Montreal study reports the plasma 25(OH)D concentration did not differ by ethnicity (white vs. non-white). This means that neither white nor non-white children in Montreal are getting much vitamin D from the sun, which is no surprise. Instead they’re getting it from their diets. Canada fortifies margarine; the U.S. and Mexico do not – but it seems unlikely that would make such a large difference. It’s a puzzle. About 47 percent of the children in this study were non-white, so it’s not a lack of data.

Now let’s move on to Figure 2, which compares two different age groups in a nationally-representative sample of Mexican children with Mexican-American children in the U.S. (In Figure 1, the data for the U.S. was for all children.)

Blog-Graphic-2What is remarkable about Figure 2 is that as the Mexican children get older, their vitamin D status improves. Note that the percentage of children above 30 is much larger, and the percentage below 20 is much smaller, in the Mexican 6-to-12 year-old group than in the 2-to-5 group. In the U.S. we see exactly the opposite; the older children – even when the group is limited to Mexican-Americans – have lower vitamin D status. In the NHANES serum 25(OH)D data for the U.S., the best vitamin D levels are in the youngest children and levels decline with age from there (although not nearly as much as people think – I’ll discuss this in a later blog). Clearly something else is going on in Mexico, which reminds us that data that are statistically representative of the U.S. population are not necessarily representative of the world population. It is also quite interesting to note that 6 to 12 year olds in Mexico, who have a mean 25(OH)D level of 42.4, are quite close to the level the vitamin D council recommends.

Figure 3 returns to the Swedish study that is shown in the fourth graph in Figure 1. That graph shows the overall results of the study. In Figure 3 the study’s results are broken down by skin color and by season.Blog-Graphic-3There are no big surprises here. Both groups of kids, who were recruited from well-baby clinics, have lower vitamin D levels in the winter than in the summer. Children with fair skin have better levels even in the winter than children with darker skin have in the summer. This study shows that skin color is a more important determinant of vitamin D status than season in the far north of Sweden as well as in the U.S, if not in Montreal.

The most frightening data I have to show you are in Figure 4.Blog-Graphic-4The data for the group of children at 41 degrees latitude, which is near Naples, Italy, come from Calcium and vitamin D intakes in children: a randomized controlled trial. At baseline there were no children with a level above 30 in this group because children with vitamin D intakes above 70% of the daily reference intake were excluded from the study. Nonetheless, the number of children with levels below 20 is quite small in comparison to most of the other studies.

Moving closer to the equator, Shanghai, China is at 31 degrees latitude. This data comes from Relationships between serum 25-hydroxyvitamin D and quantitative ultrasound bone mineral density in 0-6 year old children. The children in this study were recruited during routine health checkups. Over 58% of the children in this study have 25(OH)D levels under 20 ng/ml. This is by far the lowest vitamin D levels we’ve seen in the studies we’ve looked at so far. But things get much worse from here.

The data for the children in the third graph, at 28 degrees from the equator in New Delhi, India, are from Impact of vitamin D fortified milk supplementation on vitamin D status of healthy school children aged 10-14 years. The children in this study were recruited while attending school. Less than 3% of the children who agreed to be in the study were excluded, mostly for health reasons, although at least one was apparently excluded for having a serum 25(OH)D level over 100 ng/ml. The low vitamin D levels in this group of children are simply astounding. At baseline, 93% were below 20 ng/ml, 42% were below 10, and 8% were below 5. Only 7% were between 20 and 30 and none were above 30.

Moving even closer to the equator, just 24 degrees away at San Antonio de los Cobres, in the mountains of Argentina, (altitude 3,750 meters or 12,300 feet), we have data from Low vitamin D concentrations among indigenous Argentinean children living at high altitudes. As in India, the children were recruited from schools. In this group, the vitamin D levels are even lower than in India. Over 96% of the children are below 20 ng/ml. Over 26% are below 8 ng/ml (in this graph, the dark blue area on the first bar shows the percentage of children with vitamin D levels less than 8, rather than 10, ng/ml). Fewer than 4% have levels between 20 and 30 and none are over 30. Given that this is an isolated area where the people are likely to be genetically similar, let’s hope the scientists in Argentina take a look at the vitamin D receptor gene in this group, which is known to have variants that effect vitamin D levels.

Although it’s probably just coincidence, it’s extremely interesting that in Figure 4’s group of four studies, vitamin D status gets progressively worse the closer the children are to the equator. Since ultraviolet light is most intense at the equator, we’d expect to find just the opposite. The disastrously low levels we’ve seen in these last two groups is particularly surprising this close to the equator. If you have any thoughts about what’s going on here, from the kids in Montreal having the highest levels to the kids in New Delhi and the mountains of Argentina having the lowest, let me know in the comments.

10 Responses to Vitamin D levels in children around the world

  1. swe9845

    The blood level should be nmol/L and NOT nmol/mL

  2. Brant Cebulla

    Nice catch, corrected now. Sorry about that!


  3. logan_n@q.com

    The google scholar engine, scholar.google.com, can find many biological reports that are not indexed on Medline. In this case, terms such as
    cholecalciferol plants solanaceae
    finds papers that might resolve the puzzle. There are many local cultivars of the common solanaceae, I would suspect, and local intakes of D3 could differ. There are even plants with a glycoside of calcitriol.

  4. IAW

    So one of the questions above is “The disastrously low levels we’ve seen in these last two groups is particularly surprising this close to the equator”. My thoughts without doing a ton of research and I am not a scientist. In general it does not matter whether a child lives near the equator; it is more what “habits or lifestyles” that population has and also the amount of pollution (China). A lot of these studies also say the participants were recruited from “school”. Both the lowest levels in India and Argentina came from school populations. There is not much “sunshine” in a classroom. Although it would be easier to maintain your levels at the equator, if you do not go in the sun enough even being at the equator will not help you. As a side note while thinking about this blog article, I looked a little at Autism rates. I found a link to an article at http://dr-king.com/docs/100711_ParallelsinNewDelhiIndia_AnEpidemic_b.pdf. The title is “Parallels in New Delhi, India: An Epidemic Induced By Added Doses Of Thimerosal-Preserved Vaccines” As told by Cherry Bethel Misra, a New Delhi nursery-school principal1 and reported by Paul G. King, PhD. This goes back to a statement I made before. Take a bunch of Vitamin D deficient children and add one too many vaccines on an already “taxed” immune system and you create a problem.
    Italy may not have really high levels but when I looked really quickly seems to have low autism rates.
    I suspect the difference in Mexican children’s levels (2-5 years and 6-12 years) could simply be that as they get older they spend more time “outside” because parents can let them play outside without as much supervision as when they are younger.
    As for Montreal, in the study they stated “Nonetheless, our results are limited to children
    attending daycare in Montr´eal and not those staying at home or residing in other regions in Canada. Daycares in Montr´eal are regulated in terms of providing milk; milk policies are likely the reason for the good vitamin D status of this group.” They also stated that “Finally, capillary sampling in adults may overestimate plasma 25(OH)D by 20% compared with venous samples (35). Although the sampling bias has not been tested in young children, it is possible that our study underestimated the prevalence of vitamin D deficiency. If we assume venous values are higher by 20%, then 36.4 and 73.2% of children would have had 25(OH)D values <50 and <75 nmol/L, respectively. However, vitamin D status was almost identical to venous values for children in Canada (6–11 y) (18) and the US (1–8 y) (4), suggesting our data are valid.” I would need a Vitamin D expert to tell me if that is so. Even though they even say it is probably the “milk policy” are you still saying at those D levels it is impossible?

  5. p2j2@shaw.ca

    I concur; most likely the residents of San Antonio de los Cobres, for cultural or environmental reasons, expose little of their skin to the sun, even in summer. Peter

  6. Magic

    On the other end of the life cycle I have experienced the rehab centers, the nursing homes. I find it criminal.

    The patients are treated nicely. They are in wheel chairs for the most part. They have popcorn in the afternoon…………BUT, they get hardly any exercise and no vitamin d…….or very little.

    I have always wondered why there are so many pneumonia deaths in the summer. It would take little to change this.


  7. William Lidicker

    I suspect that the kind of clothing children wear could be a major variable, that is, how much skin exposure do they get. With this in mind it would be valuable to know if the kids were from a rural or urban environment, because this affects the amount of their outdoor activity. Also, sex should be recorded from the children (or adults) sampled especially in cultures in which the clothing (or amount of outdoor activity) for males and females is very different. It would be very interesting in this regard to sample folks from Muslim cultures, especially those living in arid environments.

  8. Brant Cebulla

    I have traveled in the Andes and for whatever reason, no matter what the temperature, people dress there in heavy clothing. If you google image search “San Antonio de los Cobres” you can get a sense of typical clothing. After centuries of dressing heavy (w/ponchos covering the entire body), you have to wonder if their bodies have adapted to suffice with lower vitamin D levels?

  9. IAW

    To Brant:
    So I googled a picture and tried to find out the life expectancy. That is when I read ” The untreated water supply in San Antonio de Los Cobres—a remote village deep in the Andes Mountains in Salta, Argentina—had a dangerously high level of arsenic.” “Arsenic levels in the tiny village reached up to 290 ppb. To put that in perspective, the World Health Organization’s maximum contaminant level for arsenic is 10 ppb”. (November 2012 http://adedgetech.blogspot.com/2012_11_11_archive.html)
    My point was going to be are they in good health wearing the heavy clothing that covers their body or in poor health. But the above put a damper on my thought process.

  10. Rita and Misty


    Your question is intriguing regarding whether the people of San Antonio de los Cobres have had their bodies adapt to suffice with lower vitamin D levels due to the typical clothing heavy clothing they’ve worn for centuries….

    I’ve heard researchers at my particular institution of employment say that vitamin d is a vestige from our hunter/gatherer days, and that our bodies have adapted to our indoor lifestyles….

    I would disagree.

    And, my disagreement is based on inverse correlation of disease to 25(OH)D levels, particularly for autoimmune diseases, breast cancer and colon cancer…

    It would be interesting to examine disease rates of the people of San Antonio de los Cobres.

    We can also look to the correlation between vitamin d serum levels and disease within the population group of Middle Eastern women (who tend to be highly covered in garb) to see if our bodies can adapt to suffice with lower vitamin d levels.

    But closer to home, we can see that the African American population as a whole is vastly deficient in vitamin d, and it suffers greatly from chronic diseases such as diabetes, high blood pressure, cardiovascular disease, MS and other autoimmune diseases, including autism, breast cancer, prostate cancer, colon cancer, etc.

    As Dr. Cannell has written about, current hunter/gather communities still have 25(OH)D levels of around 50-55 ng/ml; and, they are healthy. To me, this tends to point to such a level as being optimal.

    In my opinion, our bodies do not ever adapt to lower 25(OH)D levels.

    In other words, vitamin d is the master hormone.

    (Thanks Brant…for piquing my interest enough to post today! And, I could definitely travel with you—the Andes are beautiful)

    Be well,
    Rita 🙂

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