Vitamin D in winter: 10 micrograms a day, cod liver oil or tablets – and why the Norwegian sun no longer helps

The result is what researchers call the vitamin D winter. According to the Norwegian health portal NHI.no (updated February 2025), solar radiation in Scandinavia from October to March/April is not strong enough to trigger vitamin D production in the skin. The official Helsenorge portal puts it plainly: in Norway, the sun is too weak to provide vitamin D in the winter half of the year.

How low the sun is this week

Solar data from the Norwegian Meteorological Institute (api.met.no) show the gap between south and north on Wednesday 28 October:

• Oslo: 16.9 degrees above the horizon at midday, sun from 07:28 to 16:32.
• Trondheim: 13.4 degrees, sun from 07:45 to 16:18.
• Tromsø: 7.2 degrees, sun from 07:51 to 15:02.

At the winter solstice on 21 December, the sun reaches 6.7 degrees in Oslo and 3.1 degrees in Trondheim, while in Tromsø it does not rise at all. By comparison, at the spring equinox on 20 March this year it climbed to 30.0 degrees in Oslo and 20.3 degrees in Tromsø. The times are in standard time, which applies now that the clocks went back overnight into Sunday 25 October.

Sun height alone cannot tell you the exact day your skin stops producing vitamin D – cloud, weather and snow matter too – but it shows why the north starts from the weakest position. The dark half of the year up there does have a bright side: the 2026–27 northern lights season.

How much vitamin D should I take in winter?

According to Helsenorge (Directorate of Health, updated 20 June 2025), the recommended daily intake is 10 micrograms for children and adults and 20 micrograms for adults over 75. Some health portals, including NHI.no, set the cut-off for the higher dose at 70.

Helsenorge notes that many people will need a supplement in winter to reach the recommendation. The Directorate advises supplements for infants not given formula, pregnant women, older people and people with dark skin. NHI.no goes further, saying most people in Norway should take a vitamin D supplement during the winter months.

Babies and children over one

Infants from one week to eleven months should get 10 micrograms a day in total, and from 12 months the adult dose applies, according to NHI.no. Babies fed only on formula do not need a supplement. The Directorate does not recommend cod liver oil in the first year of life.

For older people, winter is also vaccine season – see when the flu vaccine reaches your county.

Cod liver oil or tablets – which is better?

NHI.no lists cod liver oil, vitamin D tablets and drops as options, all available without a prescription from pharmacies and supermarkets. None of the sources ranks one form above another; the recommendation is given in micrograms, whatever the source.

The Directorate’s dietary advice on osteoporosis says a teaspoon of cod liver oil or 100 grams of salmon each provide around 10 micrograms. Content varies between products, so check the label for the amount per dose.

Foods that contain vitamin D

• 100 grams of oily fish such as herring, salmon or mackerel provides a day’s dose.
• Half a litre of vitamin D-fortified semi-skimmed milk (the green carton in Norway) covers almost a third of daily needs.
• 100 grams of margarine contains 10 micrograms.
• Fruit and vegetables contain no vitamin D.

Even with a normal diet it can be hard to get enough, NHI.no warns. In the Ungkost 3 dietary survey (2015), 13-year-olds got an average of 3.9 micrograms of vitamin D a day without supplements and 7.0 micrograms with them.

What are the symptoms of vitamin D deficiency?

Usually none. Mild to moderate deficiency generally causes no symptoms, NHI.no says. Severe deficiency can cause muscle and bone pain, rickets in children – which is very rare – and softening of the bones (osteomalacia) in adults, with muscle weakness and leg pain. Beyond that, deficiency produces no clear symptoms, according to Helsenorge.

Deficiency is diagnosed with a blood test for 25-hydroxyvitamin D. Helsenorge counts 50 nmol/l or more as sufficient, 30–50 nmol/l as insufficient and below 30 nmol/l as deficient.

How common are low levels in Norway?

The Directorate’s report “Vitamin D in Norway” (National Council for Nutrition, 2018) shows the seasonal effect clearly. In the HUNT study of adults in Trøndelag (aged 19–55, data from 1995–97 and 2006–08), 64 per cent were below 50 nmol/l in winter, against 20 per cent in summer. In Tromsø, 60 per cent of first-year upper secondary pupils were below 50 nmol/l (Fit Futures, 2010–11). The report notes that measurement methods vary between laboratories.

Can you get too much vitamin D from supplements?

Yes. The European tolerable upper intake level is 100 micrograms a day for adults (including pregnant and breastfeeding women) and children aged 11–17, 50 micrograms for children aged 1–10, 35 micrograms for infants aged 6–12 months and 25 micrograms for babies under six months, according to the 2018 report. The limits were set by the European Food Safety Authority (EFSA).

An overdose raises calcium in the blood (hypercalcaemia). Chronic hypercalcaemia can lead to kidney stones and, in severe cases, kidney failure, seizures, coma and death, the report states. It also recalls that in summer 2016 more than 100 children in Denmark developed severe hypercalcaemia after being overdosed with vitamin D drops.

Nor does more bring extra benefit: the report finds no additional health gain from doses far above the recommended daily intake. If a blood test shows a low level, a doctor may prescribe higher doses for a period, Helsenorge says.

What happens when the sun returns?

In summer the sun takes over again. Five to thirty minutes of sun on the face, hands and arms a few times a week provides enough vitamin D, according to NHI.no, while daily factor 50 sunscreen on all exposed skin can cause deficiency even in summer. Sunbeds are not recommended. People who are rarely outdoors in daylight, have dark skin or cover most of their skin are at greater risk of deficiency, Helsenorge says.

Frequently asked questions

How much vitamin D should I take in winter in Norway?

The Directorate of Health recommends 10 micrograms a day for children and adults and 20 micrograms for those over 75. A teaspoon of cod liver oil provides about 10 micrograms.

Why doesn’t the sun make vitamin D in Norway in winter?

The sun is so low that UVB radiation has to travel a long way through the ozone layer and becomes too weak. In Scandinavia this applies from October to March/April, and the sun is lowest in the north.

Can you get too much vitamin D from supplements?

Yes. Adults should not exceed 100 micrograms a day, and children aged 1–10 should not exceed 50 micrograms. Too much can cause hypercalcaemia and, in severe cases, kidney failure.

Do children over one need a vitamin D supplement?

Children from 12 months are recommended 10 micrograms a day, the same as adults. Cod liver oil is not recommended in the first year of life.

Does vitamin D help against tiredness and colds?

According to Helsenorge, studies of supplements against infections, fatigue and headaches have largely shown no preventive effect. The main purpose of the supplement is to cover the body’s needs, including those of the skeleton.