Find out how the UV index, time of day, skin exposure and time in the sun impact vitamin D levels.
The sun’s UVB rays help the skin produce vitamin D, which is essential for bone health, immune function, and MS management. While Overcoming MS recommends taking vitamin D supplements, natural sunlight also has important benefits, find out more here.
In some parts of the world, at certain times of the year, you may be able to get enough vitamin D from sunlight alone. This page will tell you how to calculate how much sun exposure you need.
The amount of time you need to spend in the sun to make enough vitamin D depends on several factors, including-
The UV index measures the intensity of UV rays at a specific location and time.
A higher UV index means less time needed for vitamin D production.
Midday sun is best for vitamin D production as UVB levels are highest.
The UV index varies throughout the day, peaking at midday before dropping.
Example: If the UV index is 14 at midday, it will be around half that at 10 am and 2 pm.
The more skin exposed, the more vitamin D your body can produce.
Long sleeves and clothing block UVB rays, reducing vitamin D production.
Exposing a small area of skin for longer doesn’t help, as once a patch of skin makes vitamin D, it stops producing more for that day.
Darker skin tones (e.g. African, Afro-Caribbean, South Asian) need more sun exposure to produce the same amount of vitamin D as lighter skin tones.
Cloudy weather significantly reduces UVB exposure.
Windows block UVB rays, meaning you cannot produce vitamin D indoors, even in direct sunlight. Sitting in a sunroom or conservatory won’t work.
In cooler climates, the sun is too weak between October and March to produce enough vitamin D. If you live in a country with long winters, supplementation is essential.
Expose as much skin as possible – Areas like arms, legs, and back produce more vitamin D than just your face and hands.
Get sunlight before applying sunscreen – Even SPF 8 blocks most UVB rays, preventing vitamin D production.
Avoid burning – The right dose of sun is just short of getting some colour in the skin on each occasion. Longer exposure won’t produce more vitamin D, but it may raise the risk of other diseases, particularly skin cancer.
The UV index identifies the strength of the sun (UV radiation) from a specific location on a particular day. The higher the UV index, the less time you need in the sun:
|
Sun exposure guidelines (Midday, uncovered skin) |
|
15–20 mins → UV Index 5 (moderate) |
|
10–15 mins → UV Index 7 (high) |
|
5–7 mins → UV Index 14 (very high) |
Example
Swimming outdoors for 10 to 15 minutes, two or three times a week (with most skin exposed) can produce 10,000 to 15,000 units of vitamin D per session.
This estimate is based on a UV index of 7, typical for spring in hotter regions (e.g. Australia) or summer in cooler regions (e.g. the UK).
If you want to use a sun-bed to increase your vitamin D production on cloudy days, be aware that most sun-beds do provide a mix of UVA and UVB rays, but check to be sure before you use or buy one.
If you do use a sun-bed, limit your time and UVB intensity to about a third of what you would spend in the sun to avoid the risk of unnecessary skin damage and possible melanoma later in life.
To find out how much sun exposure you need, check the UV index forecast for your area:
| Country (City) | . | J | F | M | A | M | J | J | A | S | O | N | D |
| Argentina (Buenos Aires) | 35°S | 9 | 9 | 7 | 4 | 3 | 2 | 2 | 4 | 5 | 7 | 9 | 10 |
| Australia (Darwin) | 13°S | 12 | 13 | 12 | 10 | 8 | 8 | 8 | 10 | 11 | 13 | 12 | 12 |
| Australia (Melbourne) | 37°S | 8 | 8 | 6 | 4 | 2 | 2 | 2 | 3 | 5 | 6 | 8 | 9 |
| Australia (Sydney) | 34°S | 9 | 9 | 7 | 5 | 3 | 2 | 3 | 4 | 6 | 7 | 9 | 10 |
| Brazil (Rio de Janeiro) | 23°S | 12 | 11 | 9 | 7 | 5 | 5 | 5 | 7 | 9 | 10 | 12 | 12 |
| Canada (Vancouver) | 49°N | 1 | 1 | 3 | 4 | 6 | 7 | 7 | 6 | 4 | 2 | 1 | 1 |
| Cuba (Havana) | 23°N | 6 | 8 | 9 | 10 | 10 | 11 | 12 | 11 | 10 | 8 | 6 | 5 |
| Falkland-Islands (Port Stanley) | 58°S | 5 | 4 | 2 | 1 | 0 | 0 | 0 | 1 | 2 | 3 | 5 | 5 |
| France (Paris) | 49°N | 1 | 1 | 3 | 4 | 6 | 7 | 7 | 6 | 4 | 2 | 1 | 0 |
| Germany (Berlin) | 52°N | 1 | 1 | 2 | 4 | 5 | 7 | 7 | 5 | 3 | 1 | 1 | 0 |
| Greece (Iraklion) | 35°N | 3 | 4 | 5 | 8 | 9 | 9 | 10 | 9 | 7 | 4 | 3 | 2 |
| Japan (Tokyo) | 36°N | 2 | 4 | 5 | 8 | 9 | 9 | 10 | 9 | 7 | 4 | 2 | 2 |
| Kenya (Nairobi) | 1°S | 12 | 13 | 13 | 12 | 11 | 10 | 11 | 11 | 12 | 12 | 12 | 11 |
| Madagascar (Antananarivo) | 19°S | 12 | 12 | 11 | 9 | 7 | 6 | 6 | 8 | 11 | 11 | 12 | 12 |
| Mozambique (Maputo) | 26°S | 11 | 11 | 9 | 7 | 5 | 4 | 4 | 6 | 8 | 10 | 11 | 11 |
| Mongolia (Ulan Bator) | 48°N | 1 | 2 | 3 | 5 | 6 | 7 | 8 | 6 | 4 | 2 | 1 | 1 |
| New Zealand (Wellington) | 42°S | 7 | 7 | 5 | 3 | 1 | 1 | 1 | 2 | 4 | 6 | 7 | 8 |
| Panama (Panama) | 9°N | 9 | 11 | 12 | 12 | 11 | 11 | 12 | 12 | 12 | 11 | 9 | 9 |
| Russia (St Petersburg) | 60°N | 0 | 0 | 1 | 3 | 4 | 5 | 5 | 4 | 2 | 1 | 0 | 0 |
| Singapore (Singapore) | 1°N | 11 | 12 | 13 | 13 | 11 | 11 | 11 | 11 | 12 | 12 | 11 | 10 |
| South Africa (Cape Town) | 34°S | 9 | 9 | 7 | 5 | 3 | 2 | 3 | 4 | 6 | 7 | 9 | 10 |
| Spain (Palma de Mallorca) | 39°N | 2 | 3 | 4 | 6 | 8 | 9 | 9 | 8 | 6 | 4 | 2 | 1 |
| Sri Lanka (Colombo) | 13°N | 8 | 10 | 12 | 12 | 11 | 11 | 12 | 12 | 12 | 10 | 8 | 8 |
| Thailand (Bangkok) | 14°N | 8 | 10 | 12 | 12 | 11 | 12 | 12 | 12 | 11 | 10 | 8 | 8 |
| USA (Los Angeles) | 34°N | 3 | 4 | 6 | 8 | 9 | 10 | 10 | 9 | 7 | 5 | 3 | 2 |
| USA (New York) | 41°N | 2 | 3 | 4 | 6 | 7 | 8 | 9 | 8 | 6 | 3 | 2 | 1 |
| Vietnam (Hanoi) | 21°N | 6 | 8 | 10 | 11 | 11 | 11 | 12 | 12 | 10 | 8 | 6 | 6 |
