Vitamin D

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Recommended daily intakes for vitamins and minerals are given as an average for daily intake over a long period of time. They are the amount that is considered to meet the needs of all healthy people, or 97% of individuals. When determining the doses, it is taken into account that people's needs vary. Most people's need for nutrients is lower than this, but in some cases, individuals may need more nutrients than is ​​indicated, for example, if they have certain diseases. Recommended daily intakes are designed to plan menus and assess the nutritional value of food for groups of people (1).

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The recommended daily intakes for vitamin D are based on the work of a Nordic expert committee on vitamin D, which is set up each time the Nordic recommendations on nutrients are reviewed. The state of knowledge in the world is taken into account at all times. The recommendations aim for the recommended daily dose of vitamin D to be the amount of vitamin that maintains the desired vitamin benefit for most healthy people, according to the measurement of the concentration of vitamin D in the blood, where it is assumed that the concentration of 25-hydroxy vitamin D is at least 50 nmol /l (4).

The results of the Nordic group of experts in 2013 were to recommend 10 µg per day from the diet for all age groups except 75 years and older, where 20 µg per day was recommended (2). The World Health Organization (WHO) has recommended a lower dose of 5 µg per day for everyone under the age of 50.

When deciding on the Icelandic recommendations in 2013, national conditions were taken into account, primarily fewer sunny days in Iceland than in the neighboring countries. That is why the Icelandic recommendations are somewhat higher than the Nordic ones or 15 µg per day. The European Food Safety Authority and an expert committee of the Institute of Medicine also recommend 15 µg per day for most age groups (4, 5).

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The European Food Safety Authority sets the upper intake level of vitamin D, i.e. of daily intake over a longer period (4). The guideline levels ​​are 100 µg per day (4000 AE) for adults and children over 11 years of age, 50 µg (2000 AE) for children over one year to ten years of age, 35 µg (1400 AE) for infants (6-12 months) and 25 µg (1000 AE) for infants six months of age. Doses over the upper level should only be taken in consultation with a physician.

If adults take higher doses than 100 µg (4000 AE) per day over a longer period (a lower upper intake level is set for children), the concentration of vitamin D in the blood increases, which also increases the concentration of calcium in the blood, which can become too high (hypercalcemia ). Symptoms that may occur with elevated blood calcium include fatigue, muscle weakness, nausea, vomiting, constipation, arrhythmias, soft tissue calcification, and weight loss. The consequences of a persistent increase in calcium in the blood can also lead to the formation of kidney stones and reduced kidney function (4).

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It can be difficult to get 10 µg, let alone 15 µg or 20 µg, of vitamin D from food. As a general rule, the Icelandic diet provides 4–5 µg per day of vitamin D but can provide up to 6–10 µg per day in those who eat oily fish at least once a week and use vitamin D-fortified milk daily (8). It is also recommended to go out in the sunlight whenever possible and enjoy being outside without sunburning. It is important to consider the use of sun protection to reduce the risk of skin cancer, but with the use of sun protection, it is not possible to rely on the outdoors to ensure good vitamin D levels. 

Everyone is therefore advised to take vitamin D in the form of supplements, either fish oil or another source of vitamin D, especially during the winter but also in the summer if you always use sun protection.

There are many types of vitamin D supplements on the market. Consumers are encouraged to carefully examine the amount of vitamin D in them in order not to exceed the upper levels of safe intake.

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Vitamin D cannot be found in many food types, but fish oil and oily fish, such as herring, salmon, trout, sardines, halibut, mackerel, and egg yolks are good sources of vitamin D. Vitamin D is added, among other things, to drinking milk (vitamin D-enriched whole milk and skimmed milk), infant formulas, some baby porridges, some types of vegetable oils, and margarine.

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According to the results of a National Dietary Survey from 2019-2021, the average intake of vitamin D in adults was 21 µg/day from food and food supplements (fish oil, pearls, or tablets). Almost half of the participants did not reach the recommended daily intake. The youngest age groups (18-39 years) consumed less vitamin D than the older ones. Thus, about 75% of men and 65% of women do not meet the recommended daily intake in the youngest age group, while the figures are below 50% for the other age groups. The groups that said they never took fish oil or other sources of vitamin D consumed around 5 µg of vitamin D per day (8).

The Directorate of Health monitors regularly some of the main determinants of health but Gallup is in charge of the implementation. According to this monitoring, 61% of Icelanders consumed vitamin D supplements four times a week or more in 2021, which is a significant increase from 2019 when the percentage was 57%. It is more common for women to consume vitamin D supplements than men. Similar results were seen from the National Dietary Survey 2019-2021, where 55% of participants aged 18-80 years said they consumed vitamin D as a supplement four times a week or more.

A national survey of the diet of 6-year-old children from 2011-2012, found that only a quarter of the children received the recommended daily dose of vitamin D and that the vitamin D consumption of a quarter of the children was below the minimum recommendations (2.5 µg/ day) (9).

A study (Icelandic) published in Læknablaðið in 2020, followed children (born in 1999) in the capital area for 10 years and measured the concentration of vitamin D in the blood. It found that in all the measurements, over 60% of the children had a lower level of vitamin D (25-hydroxy vitamin D) in their blood than 50 nmol/L (10). According to information from Ískrá, published in the annual Public health indicators, 51% of pupils in the 1st grade consumed vitamin D supplements in the winter of 2021/2022.

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The same recommendations for vitamin D intake apply to pregnant and breastfeeding women as for other adults or 15 µg (600 AE) per day. If pregnant women have not been taking vitamin D supplements (eg fish oil, fish oil pearls, or vitamin D tablets) regularly before pregnancy, it is recommended to take slightly higher doses for a few weeks or equivalent to 25-50 µg (1000-2000 AE) per day. A dose exceeding the upper limit of 100 µg (4000 AE) should only be taken in consultation with a physician.

A recent Icelandic study among pregnant women showed that about 70% of the women had a concentration of vitamin D (25 hydroxy D-vitamin) above 50 nmol/L, which is considered adequate, 30% had a value below 50 nmol/L, of which there were 5 % with a value below 30 nmol/L which is defined as vitamin D deficiency (11).

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It is recommended to give vitamin D drops to infants from 1–2 weeks of age, corresponding to 10 µg (400 AE) per day, regardless of whether the child receives breast milk and/or infant formula. Since vitamin D levels in infant formulas are now higher than before, the recommendations for parents of infants exclusively fed on infant formula have been changed. If the child is fed exclusively on infant formula and receives 800 ml per day or more, it should not receive a vitamin D supplement. If the infant receives more than 800 ml of infant formula and an additional 10 µg of vitamin D in the form of vitamin D drops, the amount may exceed the safe upper level of intake. The safe upper level of intake is 25 µg per day for infants aged 0-6 months and 35 µg per day for children aged 6-12 months.

For children who receive less than 800 ml of infant formula per day, the recommendation remains unchanged, i.e. 10 µg (400 IU) of vitamin D per day via vitamin D drops.

At the age of four months, a child who feeds exclusively on infant formula can be allowed to taste small portions of other foods to increase the variety. The amount of solid food is gradually increased in line with the baby's needs, and the amount of infant formula that the baby receives is reduced. If a child has been drinking more than 800 ml of infant formula and therefore not receiving a vitamin D supplement, it is important to start giving a vitamin D supplement when the amount of infant formula becomes less than 800 ml per day. It is then recommended to give 10 µg (400 AE) of vitamin D per day as stated above.

See more information at  Heilsuvera (Icelandic)

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There has been a lot of discussion about whether vitamin D can reduce the chance of getting infected with COVID-19, see the scientific website of the University of Iceland (Icelandic). A recent editorial in the journal Lancet discusses that daily intake of vitamin D in doses ranging from 10-25 µg (400-1000 AE) for one year may reduce respiratory infections in general, particularly in those with vitamin D deficiency (12). The Public Health Agency in England has reiterated the importance of adults and children over one year of age taking a supplement of 10 µg (400 AE) daily during the winter (lower doses for infants) (13).

As mentioned before, it is recommended to take vitamin D as a food supplement in Iceland, especially during the winter. These recommendations are primarily to ensure good bone health, but could also reduce the chance of respiratory infections. There is no evidence that higher doses than the recommended daily intake of vitamin D benefit the immune system, that is, in the absence of a deficiency. However, there is evidence that it can be more difficult for people with vitamin D deficiency to fight virus infections. Vitamin D deficiency is quite common in Iceland, especially in those who do not take vitamin D supplements. It is therefore important, as always, that everyone consumes vitamin D daily.