The main function of Vitamin D in the human body is to regulate our calcium and phosphate levels. If we have good levels of these, then it helps keep our bones, teeth and muscles healthy.
If we don’t get enough Vitamin D, then this can result in some people developing bone deformities.
Where do we get Vitamin D from?
Vitamin D is found in some food, but it’s not the primary source of Vitamin D. Human beings get most of the Vitamin D they need from the sun.
The sun acts on chemicals under the skin and helps turn them into Vitamin D. Unfortunately, getting enough Vitamin D daily can be difficult in the UK and in northern climates where people spend a lot of their time indoors (and the weather’s not always the best).
Wearing an SPF, which is highly recommended to provide our skin from the sun’s harmful UV rays, can also impact our body’s ability to absorb Vitamin D. It’s also widely reported that it can take people with naturally dark skin longer to boost their Vitamin D levels in the sunshine.1 The main reason for this is that the pigment (melanin) in dark skin doesn’t absorb as much UV radiation.2
Vitamin D-rich foods
Vitamin D is present in a small selection of food. These food sources include:
- Oily fish – such as mackerel, herring, salmon, sardines
- Liver
- Egg yolks
- Red meat
- Fortified food – such as fat spreads and breakfast cereals
- Dietary supplements – while they aren’t strictly a food, they are consumed and can be used to help boost Vitamin D levels, especially between October to March, when we spend more times indoors, there’s less natural sunlight and the sun’s rays aren’t as strong as in the summer.3
How much Vitamin D do we need?
According to the latest NHS guidance, adults and children over the age of one need 10mcg (micrograms) of Vitamin D per day.
This guidance applies to everybody, including people who are at risk of having a Vitamin D deficiency and women who are pregnant or breastfeeding.
For babies who are up to the age of one, they require 8.5-10mcg of Vitamin D per day.4
Calculating Vitamin D levels
When looking at supplements, the UK guidance is in micrograms, but a lot of the labels refer to IU (International Unit) which can be a bit confusing.
To help you out, it’s worth remembering that one IU of Vitamin D is equivalent to 0.025 micrograms. Or you can use this table:5
| IU | How to calculate | MCG |
| 400IU | Divide by 40 | 10mcg |
| 600IU | Divide by 40 | 15mcg |
| 800IU | Divide by 40 | 20mcg |
| 1000IU | Divide by 40 | 25mcg |
| 2000IU | Divide by 40 | 50mcg |
Ways to boost your Vitamin D levels
Here are some food and non-food related ways you can up your Vitamin D levels:6
- Get out in the sunlight – it’s worth noting here that people with darker skin (as mentioned above) need to spend longer in the sun than people with lighter skin to produce Vitamin D. If you’re older, your skin can also be less efficient at producing Vitamin D too.
- Up your intake of fatty fish – fatty fish and seafood are among the richest natural food sources of Vitamin D around. A 100g serving of canned salmon can provide up to 386IU of Vitamin D, that’s around half of the recommended daily allowance.
- Eat mushrooms – just like humans, mushrooms can produce their own Vitamin D once they’re exposed to UV light. Humans produce a form of Vitamin D known as D3 or cholecalciferol, whereas mushrooms produce D2 or ergocalciferol.
- Eat egg yolks – not all yolks contain the same Vitamin D levels. But on the whole, research has found that eggs from pasture-raised or free-range chickens offer up to four times more — or up to 20% of the RDA. Interestingly, this depends on how long the chicken has spent outdoors in the sun.
- Use a UV lamp – UV lamps mimic the action of the sun and can be especially helpful if your sun exposure is limited because of living in limited sun areas or because you spend quite a bit of time indoors.
- Take Vitamin D supplements – supplements vary in dosage and the amount you take in supplement form will depend on your natural Vitamin D levels
What happens if you have too much Vitamin D in your body?
Something called Vitamin D Toxicity or Hypervitaminosis D, can develop. It’s a rare condition, but potentially serious if you have too much Vitamin D in your body.
Taking more than 100 micrograms of Vitamin D a day can be potentially harmful and could possibly lead to Vitamin D Toxicity.7 The condition is usually caused by taking too many Vitamin D supplements, not by diet or sun exposure. This is because the body is able to regulate the amount of Vitamin D it receives via sun exposure. Meanwhile, foods, even fortified foods, don’t contain masses of Vitamin D.
Vitamin D toxicity can lead to a build up of calcium in your blood (hypercalcemia), which can cause nausea and vomiting, weakness, and frequent urination. In some cases, Vitamin D toxicity can also cause bone pain and kidney problems, such as the formation of calcium stones.
Vitamin D doses higher that are higher than the RDA are sometimes recommended to treat medical problems, such as Vitamin D deficiency, but these are given only under the care of a doctor for a specified timeframe. During this time, the person’s blood levels should be closely monitored while they are taking such high doses of Vitamin D.8
Vitamin D intake upper level guidance
To help prevent toxicity, it’s advisable to follow these upper intake levels:9
| Age | Intake (IU) |
| 0-6 months | 1000 |
| 7-12 months | 1500 |
| 1-3 years | 2500 |
| 4-8 years | 3000 |
| 9+ years | 4000 |
Is it possible to overdose on Vitamin D?
Can you overdose on Vitamin D? It’s possible to take too much Vitamin D, given the fact the sun and our diet alone cannot provide us with the amount we need to maintain healthy Vitamin D levels.
Therefore, if you are taking Vitamin D supplements, but haven’t paid too much attention to your natural level before starting them or are taking supplements with a level of Vitamin D that’s too excessive for you, then it’s possible to take too much.10
For more Vitamin D advice, check out this article, ‘Which type of Vitamin D is best for you?’
Last updated: 9 September 2020
Sources
1 https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-how-much-vitamin-d-do-i-need/#:~:text=Mayo%20Clinic%20recommends%20that%20adults,may%20have%20additional%20health%20benefits.
2 https://www.sunsmart.com.au/uv-sun-protection/how-much-sun-is-enough#:~:text=Vitamin%20D%20deficiency&text=People%20with%20naturally%20very%20dark,absorb%20as%20much%20UV%20radiation.
3 https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
4 https://www.heartuk.org.uk/low-cholesterol-foods/vitamin-d
5 https://vitaminddrops.com/us_en/blog/research/what-does-iu-mean
6 https://www.healthline.com/nutrition/how-to-increase-vitamin-d#7.-Try-a-UV-lamp
7 https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/#:~:text=Do%20not%20take%20more%20than,than%2050%20micrograms%20a%20day.
8 https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/vitamin-d-toxicity/faq-20058108
9 https://www.news-medical.net/health/Vitamin-D-Overdose.aspx
10 https://flo.health/menstrual-cycle/health/symptoms-and-diseases/too-much-vitamin-d
