Why many vitamin D recommendations – including the Nordic - are deficient?

27.11.2024

Johanna Kaipiainen, M.Sc. (nutrition science), RD (registered dietitian)

Vitamin D recommendations vary worldwide – or precisely in the Northern hemisphere. At the southernmost latitudes, there is little need for vitamin D recommendations. There it is possible to get vitamin D all year round from the sun. The skin produces vitamin D when there is UV radiation from sunlight. Above 37ŗ latitude during the winter months there are decreases in the cutaneous production of vitamin D, because of the angle from where the sun’s rays are entering (1). The more the latitude is, the longer the duration of the winter period, when vitamin D has to be obtained from other sources than sun. For example, in Finland this period last from the beginning of October to the end of March. There are little other sources than supplements: sources of vitamin D are fish, some mushrooms, and fortified margarines, fortified milk and fortified plant-based alternatives to cow’s milk.

Different target levels lead different recommendations

However, the logic of vitamin D recommendations does not follow the latitudes. The lowest recommendation, 10 µg/d can be found in recently published Nordic Nutrition recommendations (2) and from UK, set by NHS (3). Updated Finnish nutrition recommendations will be published in November 2024 and recommendation for vitamin D will be as in Nordic recommendation. EFSA (Europeans Food Safety Authority) and IOM (Institute of Medicine, nowadays changed its name to the National Academy of Medicine) have set a vitamin D recommendation of 15 µg/d (4,5). In Central Europe Switzerland, Austria and Germany have set their vitamin D recommendation at 20 µg/d (6). The highest recommendations come from Poland (7) and Ukraine (8). In Poland the sun is taken into the account, and sunbathing is recommended for healthy adults in summertime. When sun derived vitamin is not an option, supplementation in a dose of 25 – 50 µg/d is recommended. For older seniors and for pregnant women 50 µg/d is the minimum. In Ukraine it is recommended 20 – 50 µg/d vitamin D supplementation for healthy persons and 75 – 125 µg/d for the risk groups (including for example obese, pregnant, dark-skinned persons and people over 60 years).

Main reason for different recommendations is ongoing dispute about what serum 25-hydroxyvitamin (25 OH D) level is sufficient and what is insufficient. Those who have higher vitamin D recommendations, have considered serum 25-hydroxyvitamin 75 nmol/l sufficient, and levels below that as insufficient. However, EFSA and IOM for example have considered 50 nmol/l as sufficient level leading to lower recommendations for vitamin D.

Low recommendations have faced a lot of criticism. According to Canadian statisticians, the IOM recommendation is based on erroneous statistical analysis and should be re-evaluated (9). According to them, a daily intake of 15 µg raises the population's serum vitamin D concentration only above the level of 26,8 nmol/l.

Heaney and Holick (10) wrote already in 2011 that IOM’s recommendation (15 µg/d) fails in logic, science and guidance. Failing in logic refers to nonskeletal benefits of vitamin D. These benefits have been studied for a long time, but at the time of writing the article it remained uncertain whether there might be nonskeletal benefits. If there were such benefits, what blood level could ensure them, was another question. Heaney and Holick emphasize that the correct statement would be that we know how much vitamin D is enough for bones, but do not know if it is
enough for nonskeletal benefits.

But how has IOM recommendation failed in science, Heaney and Holick explained: studies indicate that a serum level 75 nmol/l (=30 ng/ml) is closer to the bottom end of acceptable range for skeletal health (10). Additionally, studies indicate that each additional 100 IU (= 2,5 µg) of vitamin D per day raises serum 25(OH)D concentration by approximately 0,7 ng/ml (=1,75 nmol/l), not one ng/ml (2,5 nmol/l) as previously thought. Furthermore, the recommended 15 µg/d by IOM produced barely perceptible changes in overweight and obese individuals, Heaney and Holick wrote (10).

Failing in guidance refers to upper-level intake of vitamin D, which is 100 µg. According to Heaney and Holick it should be stressed that the upper limit is not a strict limit that someone should be concerned about, but instead constitutes an assurance of safety for such intake (10).

Avoiding the uncertainty about sufficient vitamin D blood level and dosage can result in weird recommendations. Recommendation of Endocrine Society has been 37,5 - 50 µg/d for adults (11), but updated recommendation published in 2024 (12) no longer endorsed the previous target 25(OH)D level of 30 ng/ml (= 75 nmol/l). As the Endocrine Society no longer endorses any specific 25(OH)D levels to define either vitamin D sufficiency or deficiency, logically it cannot set any precis recommendations about daily vitamin D dosage. However, high percentages of low vitamin D status are mentioned in its guidelines and vitamin D supplementation is recommended for children, pregnant women, adults older than 75 years and people with high-risk prediabetes. How much should these people take supplements? If any recommendation fails to guide, it is this one. Instead of recommended doses, Endocrine Society provides the dose ranges that were used in the trials cited as evidence for the recommendation. Of course, these ranges are wide.

Nowadays extraskeletal benefits of vitamin D are no longer just hypothetical, but part of some recommendations. A randomized controlled study called VITAL, with more than 25 000 participants, has studied nonskeletal benefits of vitamin D. One finding from this study was that vitamin D supplementation for five years reduced autoimmune disease by 22 %. Those who got supplementation, the dosage was 50 µg/d (13). In Finland, Current Care Guidelines, set by Finnish Medical Society Duodecim, recommend 50 µg/d to MS-patients (14). Endocrine Society’s recommendation has also considered extraskeletal benefits. Potential to lower risk of preeclampsia, intra-uterine mortality, preterm birth, small for gestational age birth, and neonatal mortality are reasons why supplementation is recommended for pregnant women. Among lifestyle
modifications, D supplementation is recommended for adults with high-risk prediabetes to reduce the risk of progression to diabetes (12).

Utterly failed recommendations

Let’s get back to the Nordic Nutrition recommendation (2), in which the vitamin D recommendation remains below EFSA and below most other vitamin D recommendations. It is interesting that most nutrient recommendations in Nordic Nutrition recommendations are in line with EFSA, but that is not the case with vitamin D. It is not even mentioned that Nordic vitamin D recommendation is lower than EFSA’s, nor is there any explanation for this in this publication. However, Nordic Nutrition recommendation did not disagree with EFSA regarding the sufficient vitamin D level in blood serum. “There is a growing agreement that circulation 25(OH) D above 50 nmol/l corresponds to sufficient levels”, the authors wrote.

Although levels below 50 nmol/l are considered insufficient, the target level in Nordic Nutrition recommendation is not set at the sufficient level. “There is convincing evidence for recommendations to be set to prevent the population from being vitamin D deficient defined as circulating 25(OH)D < 30 nmol/l.” it is also argued in Nordic Nutrition recommendation. Most definitions for deficient vitamin D level are < 50 nmol/l, but at least all agree that 30 nmol/l is not a sufficient level. But this is the level that it is possible to reach by following Nordic vitamin D recommendation.

As mentioned earlier, also in UK the vitamin D recommendation is the same, 10 µg/d. It is explained in Nordic Nutrition recommendation how UK has set this recommendation and more about this can be read from SACN (Scientific Advisory Committee on Nutrition) publication (15). SCAN has estimated the average daily vitamin D intake required to maintain serum 25(OH)D concentration ≥25 nmol/l in winter by 97.5% of the population. Depending on the analysis method, intake was 9 - 12 μg/d and this is how the recommendation was set at 10 μg/d. Maintaining level ≥25 nmol/l is also not sufficient. Taking 10 μg of vitamin D per day one can maintain his or her serum 25(OH)D concentration only at an insufficient level.

After the previous recommendations, many new randomized controlled trials have been published (16-21) about sufficient daily vitamin D intake. Findings from these studies are consistent: 10-15 μg/d is not enough to maintain serum vitamin D concentrations at sufficient levels, not even for children. All these studies have been ignored in current Nordic and Finnish nutrition recommendations.

How much vitamin D is needed?

Are vegans at a higher risk of getting vitamin D deficiency? Yes and no. Yes, if they do not supplement their diet with vitamin D. A vegan diet has fewer vitamin D sources than a mixed diet. However, vitamin D deficiency is widespread regardless of diet. Worldwide prevalence of vitamin D deficiency (concentration below 50 nmol/l) remain 24 – 49 % (22). According to Adventist Health Study the diet has not much effect on vitamin D status (23). The skin color, use of supplements and time spent in the sun were more meaningful than diet (23).

In a recent review Pludowski et al. are arguing why a daily dose of vitamin D should be 50 μg/d for adults in the general population (24). This amount is sufficient to raise and maintain serum 25(OH)D concentrations above 50 nmol/l and above 75 nmol/l in >99 % and >90 % of the general adult population, respectively. Health outcomes from observational studies support a serum 25(OH)D concentrations of 75 nmol/l and higher as the optimal level. For most endpoints these levels are superior to concentrations from 50 to 75 nmol/l (24). Supplemental dose of 50 μg/d prevents and treat vitamin D deficiency in the general population and there is no risk for getting too much vitamin D with this dosage.

Regardless of your diet, my advice for everyone who is living in the Northern Hemisphere is this:

  • Get measured your serum 25(OH) concentration during the winter at least once in your life.
  • Raise and maintain your concentration in 75 -120 nmol/l.
  • Supplement your diet with 50 – 100 μg daily vitamin D supplement. More than 50 μg/d may be needed if you are overweight, obese, pregnant or you have type 2 diabetes. But do not exceed the dose 100 μg/d.
References:
  1. Holick MF. Sunlight and vitamin for bone health and prevention of autoimmune disease,cancers, and cardiovascular disease. American Journal of Clinical Nutrition 2004:80(suppl):1678-88S.
  2. Blomhoff R, Andersen R, Arnesen EK, Christensen JJ, Eneroth H, Erkkola M, Gudanaviciene I, Halldorsson TI, Hųyer-Lund A, Lemming EW, Meltzer HM, Pitsi T, Schwab U, Siksna I, Thorsdottir I, Trolle E. Nordic Nutrition Recommendation 2023. Copenhagen: Nordic Council of Ministers 2023.
  3. NHS. Vitamin D. www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d (referred 24.1.2024)
  4. European Food Safety Authority. EFSA Journal published by John Wiley and Sons Ltd on behalf of European Food Safety Authority. https://doi.org/10.2903/j.efsa.2016.4547
  5. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
  6. Spiro A, Buttriss JL. Vitamin D: An overview of vitamin D status and intake in Europe. Nutr Bull. 2014 Dec;39(4):322-350. doi: 10.1111/nbu.12108. PMID: 25635171; PMCID: PMC4288313.
  7. Płudowski P, Kos-Kudła B, Walczak M, Fal A, Zozulińska-Ziółkiewicz D, Sieroszewski P, Peregud-Pogorzelski J, Lauterbach R, Targowski T, Lewiński A, et al. Guidelines for Preventing and Treating Vitamin D Deficiency: A 2023 Update in Poland. Nutrients. 2023; 15(3):695. https://doi.org/10.3390/nu15030695
  8. Grygorieva N, Tronko M, Kovalenko V, Komisarenko S, Tatarchuk T, Dedukh N, Veliky M, Strafun S, Komisarenko Y, Kalashnikov A, et al. Ukrainian Consensus on Diagnosis and Management of Vitamin D Deficiency in Adults. Nutrients. 2024; 16(2):270. https://doi.org/10.3390/nu16020270
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  11. Holick MF, Binkley NC, Bischoff-Ferrari A, Gordon CM, Hanley DA, Heaney RP, et al. Clinical practice guideline: evaluation, treatment and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism 2011; 96:1911-30.
  12. Demay MB, Pittas AG, Bikle DD, Diab DL, Kiely ME, Lazaretti-Castro M, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2024 Jul 12;109(8):1907-1947. doi:10.1210/clinem/dgae290. PMID: 38828931.
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  14. MS disease. Current Care Guidelines. Working group set up by the Finnish Medical Society Duodecim and the Finnish Neurologic Association. Helsinki: The Finnish Medical Society Duodecim. Helsinki: Suomalainen Lääkäriseura Duodecim, 2024 (referred 9.10.2024). Available online at: www.kaypahoito.fi
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