🧪 Vitamin D

Vitamin D is a fat-soluble vitamin that helps the body absorb calcium and phosphorus and supports healthy bones. The skin makes it itself in direct sunlight: in Britain, from late March or early April to the end of September most people get enough, while from October to early March the sun is too weak (NHS).

Milk itself contains little vitamin D, so some countries add it at the dairy (fortification). Fortification of cow’s milk began in the early 1930s and greatly reduced rickets in children. In Britain, however, cow’s milk is usually not fortified, and the NHS does not count it as a good source. Check the package to see if your milk has vitamin D.

From food, vitamin D comes from oily fish (salmon, sardines, trout, herring, mackerel), liver, egg yolks, red meat and fortified foods such as some fat spreads or breakfast cereals. A deficiency causes rickets in children and osteomalacia, with bone pain, in adults.

The NHS advises children from one year old and adults to get 10 µg (400 IU) a day, and many people to take a supplement in autumn and winter. EFSA gives 15 µg a day as an adequate intake for people from one year. The upper limit for adults and children aged 11–17 is 100 µg (4000 IU) a day, for children aged 1–10 it is 50 µg. Too much from supplements over a long time can lead to hypercalcaemia, which weakens bones and harms the kidneys and heart.

Vitamin D from milk or from a supplement? They are not the same source. Milk itself contains little vitamin D, so some countries add it at the dairy; that fortification began in the early 1930s and greatly reduced rickets in children. Skin makes it in direct sunlight, and food adds it through oily fish, liver and egg yolks. A supplement gives a measured dose but has an upper limit you should not exceed. Milk is therefore not a guaranteed source, so check the label.

Ordinary drinking milk has one ingredient, so it does not have to carry an ingredient list, but added vitamin D would show on the pack: look for “vitamin D” or “fortified” in the name or ingredients. Amounts are given in µg or IU, and 10 µg equals 400 IU. Milk with added vitamin D sits in the chilled dairy aisle of a supermarket, while supplements are sold at pharmacies; discuss the dosage with a doctor.

Why it matters to you. Do not treat milk as a guaranteed source of vitamin D: countries fortify it differently, in Britain usually not. Check the ingredients, and do not exceed the upper limit if you take supplements; discuss dosage with a doctor.