When can you get vitamin D from the sun? A month-by-month calendar for the UK and Europe

What the vitamin D sunlight calendar shows

The calendar works out how high the sun climbs at midday in the middle of each month and colours the months in three bands:

• enough sun – the sun is above 40°;
• little sun – 30–40°;
• almost no vitamin D made – the sun is below 30°.

Your skin makes vitamin D from ultraviolet B (UVB) light. When the sun is low, its light takes a long slanting path through the atmosphere and very little UVB gets through. You can walk for an hour on a clear January day and make almost no vitamin D.

How to use the calendar

1. Pick your city from the tabs. If yours isn’t listed, choose the nearest one at a similar latitude.
2. Look at the colour of each month and the sun angle shown under it.
3. Read the summary: how many months have too little sun.
4. Use it to decide when to start your vitamin D and when you can stop.

How to read the result

For London, the calendar lines up with NHS advice: from October to March the sun is too weak to make enough vitamin D. Further north, in Edinburgh or Dublin, September is already borderline. Cardiff is at about London’s latitude, while Manchester and Belfast sit between London and Edinburgh.

A quick check without the calendar: look at your shadow at midday. If it’s longer than you are tall, the sun is below 45° and there’s little UVB.

Why you may fall short even in summer

A high sun is only one condition. These also cut how much vitamin D you make:

• cloud and smog;
• clothing that covers most of your skin;
• sunscreen: SPF 8 or higher blocks much of the UVB that makes vitamin D;
• glass: no vitamin D is made through a window;
• age: older skin makes less;
• dark skin, which needs longer in the sun.

That’s why the NHS advises some groups to take vitamin D all year round. Find your situation:

Limits of the calendar and when to see a doctor

• It’s an estimate based on the midday sun angle. It doesn’t allow for cloud, altitude or how long you spend outdoors.
• It assumes you’re outside. A sunny desk by the office window doesn’t count: UVB doesn’t pass through glass.
• It doesn’t tell you your vitamin D level. Only a 25(OH)D blood test does.
• Don’t sunbathe for vitamin D: UV raises the risk of skin cancer. Never let your skin redden or burn.
• Don’t take more than 100 mcg (4,000 IU) a day unless your doctor advises it. If you have sarcoidosis, kidney stones or kidney disease, or take thiazide diuretics, discuss the dose with your GP.
• For children, the NHS sets lower maximums: 50 mcg a day for ages 1–10 and 25 mcg for babies. Follow the label and your health visitor or GP.

How to choose vitamin D3 on iHerb

1. Check in the calendar how many months your city is short of sun.
2. Choose a dose for those months: the NHS recommends 10 mcg (400 IU) a day. More detail is in our guide to how much vitamin D3 to take.
3. If the label gives the dose in IU and you want mcg, use the IU to mcg converter: 1 mcg = 40 IU.
4. Compare drops and softgels by cost per day.
5. If you also take a multivitamin, add up the vitamin D in every product.

For other supplements worth thinking about when the clocks go back, see vitamins to take in winter.