Vitamin D for adults: how much is enough and how to take it properly

Tuesday morning, mid-October. A woman in her forties walks into the pharmacy and asks me: something for energy? She adds that she sleeps enough, yet wakes up tired, and as the day goes on even the stairs become an effort. After a deeper conversation and a question I ask quite often at this time of year: when did you last have a test measuring your vitamin D? Her answer was: I have never had one. She came back a few days later with the blood test result and a visit to the doctor: 28 nmol/L, a clear deficiency. Her case is not an exception but the rule I see repeated every autumn.

This article holds everything I explain about vitamin D to the people who come into the pharmacy from September onwards: almost all of Bulgaria enters the winter season with empty reserves, which test gives the answer and how to read it, how much vitamin D is enough and how to take it so your body absorbs it. And also when fatigue is not about a lack of vitamin D and when a supplement only masks the real cause.

The largest Bulgarian study on the subject comes from a team of the Bulgarian Society of Endocrinology with 2,032 people from across the country. The result: 75.8% of participants had vitamin D deficiency or insufficiency, and severe deficiency among women reached 26.9% (Borissova and colleagues, International Journal of Clinical Practice). Levels are lowest at the end of winter and in early spring, exactly when the summer reserves run out.

The reason is geographic and beyond our control. Bulgaria sits between 41 and 44 degrees north latitude, and from October to April the sun stands so low that the UVB rays needed for vitamin D synthesis in the skin practically do not reach us in sufficient amounts. Even a sunny December day outdoors produces almost nothing. Personal factors add to this: darker skin synthesises more slowly, after the age of 65 the skin produces about a quarter of the youthful amount, and with excess weight the vitamin gets trapped in fat tissue and less of it reaches the blood.

In summer, 10 to 15 minutes of sun exposure around noon with bare arms and legs is enough for fair skin to obtain the daily dose. Dark skin needs three to six times longer for the same result. The detail that surprises people most: glass blocks UVB rays completely. Driving, working by a window and drinking coffee in a cafe at a table behind a glass storefront produce no vitamin D, however sunny it is outside.

There is something else interesting to say on the topic: sunscreen applied properly blocks most of the synthesis. But that is not an argument against it, because skin pays for burns at a higher price than it gains in vitamin, and in autumn and winter the sun at our latitude is not a source for obtaining it anyway. I write about proper protection in detail in the article on the sun protection factor. The conclusion: from October to April, taking vitamin D from the pharmacy is not a whim but a seasonal need for most of us.

Low vitamin D levels often overlap with: fatigue, muscle aches, frequent infections, restless sleep. Each of these complaints has a dozen possible causes. That is why the internet lists people use to diagnose themselves are not only a clever marketing trick but also dangerous. The only honest answer comes from the blood test called 25-hydroxyvitamin D, or 25(OH)D.

The result is read in nanomoles per litre. The practical frame: below 30 nmol/L is deficiency, between 30 and 50 is insufficiency, between 50 and 125 is a satisfactory level. Above 125 nmol/L (above 50 ng/mL) is the boundary beyond which higher concentrations bring no additional benefit and can lead to unwanted effects with long-term intake. Above 250 nmol/L (above 100 ng/mL) is defined as hypervitaminosis D (elevated blood calcium levels, so-called hypercalcemia), and above 375 nmol/L (above 150 ng/mL) is classified as vitamin D intoxication, which requires medical supervision (IOM, 2011; Endocrine Society; NIH). Mind the units: some laboratories report in ng/ml, and 1 ng/ml equals 2.5 nmol/L, so 30 ng/ml and 30 nmol/L are very different results. Interpretation and the decision on dose are a doctor's job.

The US Institute of Medicine sets 600 IU daily for adults up to 70 years and 800 IU above that age (IOM, 2011). The Endocrine Society gives a higher frame for maintaining good levels: 1,500 to 2,000 IU daily. Bulgarian endocrinologists recommend that adults here take between 800 and 2,000 IU daily during the autumn-winter period, depending on baseline level, weight and age. The upper limit set by EFSA is 4,000 IU per day for adults, and it is not to be exceeded long-term without medical supervision.

What is the label allowed to say in the EU? Vitamin D carries several approved claims under Regulation (EU) No 432/2012: it contributes to normal absorption of calcium and phosphorus, to the maintenance of normal bones, teeth and muscle function, and to the normal function of the immune system. Read them carefully: normal function is maintenance, not treatment of a disease. A label promising more than this is outside the law.

On the label, look for one more word: cholecalciferol. This is the D3 form that our skin produces itself. A meta-analysis of the randomised trials shows that D3 raises the concentration in the blood more effectively than D2 at the same dose (Tripkovic and colleagues, American Journal of Clinical Nutrition, 2012).

Vitamin D is fat-soluble, and that settles half the question. A study cited by the NIH measured up to about 50% higher blood levels when the dose is taken with a meal containing fat, compared with intake on an empty stomach (Mulligan and Licata, 2010). This is how to take it: the drops or the capsule are taken at breakfast or lunch with an egg, yoghurt, avocado or olive oil, not with a sip of water on an empty stomach. The hour of intake has no proven significance, but regular intake does.

Daily and weekly schedules give similar levels when the total dose is equal. Giant single doses are a different story. A study known as the Vital D study, led by Dr Kerrie Sanders, shows that giving a huge single dose of 500,000 IU of vitamin D3 once a year to women aged 70 and over not only does not protect against fractures but increases the risk of falls and fractures (JAMA, 2010). Megadoses taken at once are ineffective and harmful to the skeletal system in elderly people.

And one combination with vitamin D that is rarely mentioned: magnesium is a cofactor (a helper molecule) of the enzymes that convert vitamin D into its active form. With chronically low magnesium, vitamin D can be ineffective, because the body fails to convert it into its useful active form. Which form of magnesium makes sense and why, I cover in the article on magnesium. And the fashionable combination with vitamin K2? Vitamin K has approved claims for normal blood clotting and the maintenance of normal bones. But in healthy people with a balanced diet, additional K2 intake aimed at the proper delivery of calcium to the bones remains a hypothesis from basic science, not a normatively approved medical fact in the EU.

I work by a window, the sun is enough for me. Well, NO: glass blocks exactly the rays that produce vitamin D. By the window you get light and warmth, but no synthesis.

I was once prescribed a huge dose, I will buy it again. This is a mistake you should not make, because treatment schemes with high doses are therapy that the doctor prescribes according to control blood tests. Repeating them from memory, without measuring, can take you from deficiency into overload.

Vitamin D cures depression. Studies find a link between low levels and mood, but there is no approved claim for treating depression and a supplement does not replace therapy. If you have a problem with your mood and it worries you, talk to a doctor.

Fatigue is the least specific complaint in medicine. Behind it may stand anaemia, the thyroid gland, sleep apnoea, diabetes and others. If fatigue lasts for weeks, the sensible first step is a visit to the doctor: they will order tests such as a complete blood count, ferritin and thyroid hormones, not a vitamin D supplement taken on your own judgement because you read on the internet that it helps with fatigue. A supplement taken blindly sometimes simply masks the symptoms and postpones the diagnosis.

There are also conditions in which vitamin D is taken only after a talk with a doctor: kidney stones or elevated blood calcium, sarcoidosis and other granulomatous diseases (a group of conditions in which the immune system creates small inflammatory nodules called granulomas in various organs), severe kidney impairment, primary hyperparathyroidism, as well as intake of thiazide diuretics or digoxin. During pregnancy and breastfeeding every supplement is agreed with the doctor. For the youngest ones the rules are separate and I cover them in the article on vitamin D for babies.

An honest answer, the kind you expect from this site: vitamin D for adults is not yet in my selected product list. The catalogue is filled only with products for which there is feedback that they truly deliver what the label says, and I am currently negotiating with several companies to provide a link. When I add a product for adults, it will carry the D3 form, a clearly stated dose and a label that I would choose for myself.

If you are hesitating between two products on the shelf or are unsure how to read your result, write to me in the chat. I answer personally and free of charge, with informational purpose, without diagnosis and without changing therapy.

This article was written by Donka Arabadzhova, Master of Pharmacy, and confirmed by the following sources: Borissova A.M. and the Bulgarian Society of Endocrinology team, study of vitamin D status in 2,032 Bulgarians, International Journal of Clinical Practice; Institute of Medicine, Dietary Reference Intakes for Calcium and Vitamin D, 2011; Holick M.F. et al., Journal of Clinical Endocrinology and Metabolism, 2011 (Endocrine Society guidelines); EFSA opinion on the tolerable upper intake level for vitamin D (EFSA Journal 2012;10(7):2813); Regulation (EU) No 432/2012 (approved health claims for vitamin D); Tripkovic L. et al., American Journal of Clinical Nutrition, 2012; Mulligan G.B., Licata A., Journal of Bone and Mineral Research, 2010; Sanders K.M. et al., JAMA, 2010; NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals.