Low vitamin D: A practical guide to correct a common problem
May 25, 2020
Low levels of vitamin D (25 hydroxy-cholecalciferol or "25OHD" in blood tests) has become an "epidemic" worldwide, affecting more than half of the global population. The UK, unfortunately, is not an exception.
Low levels of vitamin D (25 hydroxy-cholecalciferol or "25OHD" in blood tests) has become an "epidemic" worldwide, affecting more than half of the global population. This is a problem in all age groups, but is especially common in older people who have suffered from an osteoporotic fracture, where low vitamin D levels extend to almost 100% of cases. A global analysis showed that 88% of the blood samples evaluated, had vitamin D levels below 30 ng / ml (insufficient); 37% were below 20 ng / ml (suboptimal) and up to 7% had values less than 10 ng / ml (deficient).
The UK, unfortunately, is not an exception: vitamin D can be produced by the body with sun exposure, but this synthesis is scarce in winter and spring. In addition, lack of dietary intake, overuse of sun protection in summer (protection factor creams greater than 8 significantly prevent synthesis), more pigmented skin or the use of some drugs, contribute to the low vitamin D levels. In our country, as in the rest of the world, vitamin D insufficiency or even deficiency, is already detected in children or young people, and persists in adults, postmenopausal women (osteoporotic or not) and the elderly.
Why are low vitamin D levels bad?
Vitamin D is necessary in the body to absorb certain micronutrients (calcium, phosphorus), closely linked to bone health and other metabolic processes. A lack of vitamin D can cause diseases such as osteoporosis in adults (especially in postmenopausal women) or rickets in children. Furthermore, low levels of vitamin D have been associated with obesity, type 2 diabetes mellitus, an increased cardiovascular risk, chronic pain, irritable bowel syndrome and an increased risk of dementia in advanced ages. Vitamin D also plays a function in the immune system, and several studies have reported that vitamin D supplementation can reduce susceptibility to respiratory infections.
We get most of our vitamin D from skin synthesis, and, to a lesser extent, from food (10-20%). Vitamin D3 or D2 is first hydroxylated in the liver, causing 25-hydroxy-cholecalciferol (25OHD), also called calcifediol or calcidiol. Next, another hydroxylation occurs in the kidney, generating 1,25 dihydroxy-vitamin D (1,25OH2D), the most hormonally active metabolite.
How can I tell if my vitamin D levels are too low?
Most people will have low vitamin D levels for a long time without even knowing it. For instance, osteoporosis, or brittle bones, is especially common in postmenopausal women but may not be diagnosed until when a fracture occurs. This can happen after decades of insufficint vitamin D levels. The best way to find out your level of vitamin D is via a blood test. But be mindful of at what time of the year you take the test. Because most of our vitamin D is produced by the skin when exposed to sun, you can normally expect your levels to be at their highest in the autumn, at their the lowest in early spring.
Given the importance of vitamin D to our health, clinical guidelines recommend correcting an insufficiency, if detected, as quickly as possible. The minimum daily intake is 400-800UI (International Units) / day, but this has proven insufficient for adults (these intakes can NOT maintain circulating levels of 50-75nmol / L, or 20-30 ng / mL, in your body). Recent studies suggest that the safe upper limit is more than 10,000 IU / day, something difficult to achieve only through diet. General recommendations are to increase sun exposure and to include foods rich in or fortified with vitamin D: fish (mackerel, tuna, sardines), cod liver oil, eggs, milk, mushrooms and general seafood. As an example, a glass of cow's milk provides about 100 IU of vitamin D, a can of tuna about 300 IU, and an egg about 120 IU.
Supplementation is recommended in case of detecting gross deficiencies (that is, less than 20 ng / ml; or between 20 and 30 ng / ml in individuals at risk: the elderly, in previous cases of osteoporosis fractures, people with skin problems or concomitant diseases, who can not leave the house, as well as children under the age of four, pregnant and lactating mothers).
However, there is controversy in the medical and scientific community about the most effective forms of vitamin D supplementation. If you have tried to increase your levels of vitamin D through generic supplements, without paying much attention to its formulation or bioavailability, the result can be poor. The best way to find out how well vitamin D supplementation is working for you is to take a follow-up blood test after a few months.
General recommendations for oral vitamin D supplementation
If you have looked at the table of empirical medical treatments proposed for hypovitaminosis D, it is evident that there are a wide number of options. If your Melio test clearly shows a deficiency, you should see your doctor, as you may require specific help and require a prescription of supplements. Always consult your doctor before starting any type of vitamin supplements as a nutritional deficiency treatment.
In the case of mild insufficiency or suboptimal levels, a moderate supplement of 1,000-2,000 IU / day of vitamin D3 should be sufficient to maintain adequate levels. Higher doses, based on body weight, are between 20-80UI / kg / day. Keep in mind that vitamin D3 (cholecalciferol) supplementation is preferable to D2 (ergocalciferol), since D3 can be used more efficiently by the body. Vitamin D is also a fat-soluble vitamin: this implies that it should be taken with meals or a source of dietary fats, such as fish oil (fat is an essential macronutrient for vitamin D metabolism).
Vitamin D's own physiology offers us various alternatives for supplementation. With approximately 1,000 IU / day, 50% of the population is able to reach 75 nmol / L circulating, and with 1,700 IU / day, up to 95%. Supplementation with higher doses, up to 2,000-10,000 IU, does not appear to provide additional benefits, but is also not toxic. The body is able to metabolize up to 3000-5000UI (in men) and, interestingly, the body stops synthesizing vitamin D through sun exposure at levels equivalent to 10,000UI.
Maintenance doses are more effective in the low ranges: at low doses, 100UI increases serum vitamin D by 1-2 nmol / L, 1,000UI by 10-25nmol / L and 2,000UI by 20-50nmol / L. This increase decreases at higher doses, since intestinal absorption decreases sharply.
Can too much vitamin D be dangerous?
20,000 IU daily has been associated with toxicity (it is recommended not to exceed 10,000 IU daily!). As medical treatment, weekly or monthly “boluses” (very high intakes) are usually proposed, and in this case the 300,000 IU should not be administered acutely.
Finally, keep in mind that, if your goal is only to maintain adequate levels, it is not recommended or necessary to take high doses initially (50,000-100,000 IU in some studies), since a normal daily supplement is just as effective.
NOTICE: This informative article is based on the bibliographic sources cited below and has been reviewed by the Melio Reviewers Committee. All content is valid as of the date of publication, but may not include more recent information. This blog is presented for information purposes only and does not constitute the practice of Medicine, Nursing or other professional health services, including the provision of medical advice, and therefore does not constitute a doctor-patient relationship. The use of information or materials linked from this blog are under the responsibility of the user. The content of this blog is not intended as a substitute for medical advice, diagnosis or treatment.
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Bischoff-Ferrari, H. A., et al. (2006). "Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes." 84(1): 18-28.
Cranney, A., et al. (2008). "Summary of evidence-based review on vitamin D efficacy and safety in relation to bone health." 88(2): 513S-519S.
Dawson‐Hughes, B., et al. (2013). "Meal conditions affect the absorption of supplemental vitamin D3 but not the plasma 25‐hydroxyvitamin D response to supplementation." 28(8): 1778-1783.
Glade, M. J. J. N. (2012). "A 21st century evaluation of the safety of oral vitamin D." 28(4): 344-356.
Grant, W. B., et al. (2010). "Health benefits of higher serum 25-hydroxyvitamin D levels in The Netherlands." 121(1-2): 456-458.
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Navarro Valverde, C. and J. J. R. d. O. y. M. M. Quesada Gómez (2014). "Deficiencia de vitamina D en España:¿ realidad o mito?" 6: 5-10.
Papaioannou, A., et al. (2011). "A randomized controlled trial of vitamin D dosing strategies after acute hip fracture: no advantage of loading doses over daily supplementation." 12(1): 135.
Rigueira García, A. I. J. R. E. d. S. P. (2012). "Recomendaciones sobre suplementos de vitamina D y calcio para las personas adultas en España." 86(5): 461-482.
Varsavsky, M., et al. (2017). "Recomendaciones de vitamina D para la población general." 64: 7-14.
Vieth, R., et al. (2007). The urgent need to recommend an intake of vitamin D that is effective, Oxford University Press.
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WHO commentary "Vitamin D for prevention of respiratory tract infections", https://www.who.int/elena/titles/commentary/vitamind_pneumonia_children/en/
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