How much vitamin D do you need in winter?

During the Swedish winter, the skin produces no vitamin D. The sun is too low between October and March for UVB radiation to arrive with sufficient strength, regardless of how long you spend outdoors. A walk in clear January weather can do a great deal for your mood, but nothing for vitamin D levels. This is why Swedish recommendations make a clear exception for vitamin D to the principle that a varied diet meets nutritional needs.

Why stores run down during winter

The body stores vitamin D in fat tissue, and the reserves built during summer last for some time into autumn. How long depends on how much sunlight you actually received, what you eat and your body composition.

For most people, levels gradually fall through winter and are lowest near the end of the period, in February and March. This is also when many start wondering whether fatigue, slow recovery or repeated colds are connected with something.

Food contributes but often does not provide the whole amount. Oily fish such as salmon, herring and mackerel are the best sources, with eggs and fortified dairy products and spreads adding a little more. Reaching recommended levels through diet alone generally requires oily fish several times a week, which few people maintain throughout winter.

What official recommendations say

The Swedish Food Agency recommends 10 micrograms a day for most adults. From 75 years of age, or with little or no sun exposure, the recommended total intake is 20 micrograms. The recommended supplement amount also depends on diet. In international units, these quantities are 400 and 800 IU respectively, because one microgram equals 40 IU. This conversion is useful because packaging uses both forms and the figures look dramatically different.

Needs increase if you rarely see daylight, work nights, cover your body for cultural or practical reasons, or have darker skin. More melanin requires longer sunlight exposure for the same skin production, which matters greatly at a latitude where sunlight is already limited. If you belong to one of these groups, a blood test helps establish your actual level rather than leaving you to guess.

Always read the dose on the packaging and add up all intake, including fortified foods. Vitamin D is fat-soluble and stored in the body, unlike vitamin C, for example, where excess is excreted. More really is not better, and long-term high doses are not something to experiment with on your own.

Take it with fat

Vitamin D is fat-soluble and is absorbed considerably better with a meal containing fat. You do not need much. Eggs, avocado, cheese, a little butter or a handful of nuts are enough.

Breakfast therefore works well for most people and is one of the day's most stable anchors. Taking the capsule on an empty stomach or with a fat-free meal means you absorb less of the same dose.

Many people combine D3 with K2 because the two work together in the body. They are available in one product if you want a simple routine, saving both a container and a step in the morning.

Build a routine that lasts throughout winter

The best routine is one you do not need to think about. Link the dose to breakfast or another established habit so it continues even when weeks become stressful and other things slip.

Set a start date as the darker months arrive and maintain the routine throughout the period instead of taking the supplement sporadically when you remember. Consistency over months determines what you get from it, rather than isolated days. As daylight returns in April, sunlight gradually takes over again.

Also read: How much vitamin D do you need per day?