If you live in Aberdeen, this is the week the vitamin D advice switches on. From October to March the sun in Scotland is too weak for your skin to make vitamin D, whatever the weather is doing, and the NHS and the Scottish Government both say the same thing: everyone should consider a daily supplement of 10 micrograms until the end of March. This guide explains why Scotland is different, exactly what the advice says, who should take a supplement all year round, and how much is too much.

Why the sun in Scotland is not enough from October to March

Your body makes most of its vitamin D in the skin, from direct sunlight. The part of sunlight that does the work is a band of ultraviolet light called UVB, and how much of it reaches you depends on how high the sun climbs. Aberdeen sits at 57 degrees north, further north than Moscow, and between October and March the sun stays so low in the sky that almost no UVB gets through, even on a clear, bright day. A sunny lunchtime walk in January feels good, but your skin is not making vitamin D on it.

That is why the Scottish Government's advice is worded the way it is: between April and September, sunlight in Scotland generally provides enough vitamin D for most people. From October to March it does not, and we depend on what we eat and on supplements instead.

What the NHS and the Scottish Government advise

The advice is the same from both. Children from the age of one and adults need 10 micrograms of vitamin D a day, and during the autumn and winter everyone, including pregnant and breastfeeding women, should consider taking a daily supplement containing 10 micrograms. On a supplement label that is sometimes written as 400 IU, which is the same amount.

Babies are a special case. Breastfed babies should have a daily supplement of 8.5 to 10 micrograms from birth, all year round. Formula-fed babies do not need one unless they are having less than 500ml of formula a day, because infant formula already has vitamin D added. Children aged one to four should have a daily 10 microgram supplement all year.

Some adults and older children should also take a supplement for the whole year, not just the winter months, because they cannot rely on summer sunlight either:

people who are rarely outdoors, for example anyone who is frail, housebound or living in a care home;
people who usually wear clothing that covers most of their skin when outdoors;
people with dark skin, for example of African, African-Caribbean or South Asian background, whose skin makes less vitamin D from the same amount of sunlight;
in Scotland, pregnant and breastfeeding women and all children under five.

If you are in one of those groups, the switch from winter to summer does not apply to you: the advice is a daily 10 microgram supplement throughout the year.

What vitamin D does, and what happens when you run low

Vitamin D contributes to the maintenance of normal bones, normal muscle function and the normal function of the immune system. In plainer words, it helps the body regulate calcium and phosphate, the two minerals that keep bones and teeth hard and let muscles work properly.

When levels stay low for a long time, the NHS says the result can be bone deformities such as rickets in children, and bone pain from a condition called osteomalacia in adults, where the bones soften. Short of that, low vitamin D has no reliable symptoms of its own. Tiredness, aches and low mood all have many possible causes, which is why guessing is not useful. If you are worried about your levels, your GP can arrange a blood test, and that is the only way to know.

Can you get enough from food?

Only a few foods contain much vitamin D, which is why the advice reaches for a supplement rather than a shopping list. The useful sources are oily fish such as salmon, sardines, herring, trout and mackerel, red meat, liver (not in pregnancy), egg yolks, and foods that have had vitamin D added, such as some fat spreads and breakfast cereals. Cow's milk in the UK is generally not a good source, because unlike in some countries it is not fortified.

A couple of portions of oily fish a week is good for you for many reasons, but for most people it will not get them to 10 micrograms a day through the winter on its own. Food plus a small daily supplement is the realistic plan.

How much is too much?

More is not better. Vitamin D is stored in the body, and taking high doses over a long period can raise calcium levels, which can weaken bones and damage the kidneys and heart. The NHS says not to take more than 100 micrograms (4,000 IU) a day as an adult unless a doctor has told you to; the limit is 50 micrograms a day for children aged one to ten and 25 micrograms for babies under one. The standard 10 microgram supplement sold in any supermarket or pharmacy sits well inside those limits, and for most people it is all that is needed.

Not sure where to start? Book a free call

If you are unsure whether the advice applies to you, what to buy, or whether your tiredness is worth a blood test, our Nutrition and Wellbeing service at the clinic in Bridge of Don starts with a free 15-minute phone call. We talk about your diet, your lifestyle and how you have been feeling, and suggest next steps that suit you: simple changes to what you eat, a supplement you can buy over the counter, a visit to your GP, or other support we offer at the clinic. There is no obligation, and if the right answer is "see your GP", we will say so. You can also reach reception on 01224 707877 or through the contact page.

Sources

This article is general information, not personal medical advice. Always speak to your GP about ongoing or worrying symptoms, and follow their advice on supplements if it differs from the general guidance above.