The NHS also recommends that people aged 65 and over, and those who do not get adequate exposure to sunlight should consider vitamin D supplementation.
Vitamin D deficiency can result in bone pain and muscle weakness. Low blood levels of this vitamin are linked to memory problems in older adults, and an increased risk of heart disease.
According to Margaret Rayman, Professor of Nutritional Medicine at the University of Surrey, while there is a risk of taking too much vitamin D, people in northern climates should supplement with 10 micrograms a day during the darker months.
There are inadequate amounts of the vitamin produced by the skin in winter because it is only made when the skin is exposed to sunlight.
Professor Rayman adds that we must not overdo vitamin D supplementation because that can cause poor appetite, nausea and vomiting.
She also recommends that some people should consider taking two other supplements – iodine and selenium. The professor has published research in the medical journal The Lancet which shows that iodine deficiency during pregnancy may damage children’s mental development.
Alarmingly, her study of more than a thousand pregnant women found that more than two-thirds were deficient. She therefore urges pregnant women, and women likely to become pregnant, to ensure that they get enough iodine.
She says: “Normally, people can get iodine from milk, dairy and fish, but there is a deficiency danger with teenage girls who consume lots of fizzy drinks and very little dairy products.”
Selenium is another vital mineral that can be lacking in the diet in countries like the UK and New Zealand. There, selenium is low in abundance in the soil on which food is grown.
Deficiency can harm the immune system and fertility in both sexes. Studies show that selenium deficiency increases premature death from all causes.
Professor Rayman says: “If you eat a lot of fish, you won’t need selenium supplementation. But you might if you don’t eat fish, Brazil nuts, or meat.”
The Dangers of Overdosing
Both iodine and selenium supplements carry a real and serious danger of overdosing. Professor Rayman says that people who worry about their vitamin intake often overdo it with supplements.
Iodine supplements are made from the seaweed kelp, which contains very high levels of the mineral. Excessive iodine intake can damage the thyroid gland, thus causing iodine deficiency problems anyway.
Too much selenium can lead to selenosis, which can cause hair loss, nausea, fatigue, nerve damage, and even heart attacks and kidney failure, says the professor.
She says: “Instead if you want to increase your selenium intake, take a combined multivitamin and mineral with low levels of ingredients. For example, with 30-50 micrograms of selenium, and 140-150 micrograms of iodine.”
Health experts agree that taking supplements is not as healthy as obtaining nutrients naturally from food, which contains other health-boosting substances such as dietary fiber.
The professor says: “Have a balanced diet. If you do that, you should be fine with all your vitamins. In the UK, perhaps vitamin D supplementation in winter should be considered, and selenium if you’re not a fish-eater.”