Vitamin D Sources
When our ancestors were living in the tropics, sunlight-on-skin was their main source of vitamin D. When sunlight shines on skin it produces vitamin D3.
Actually, only a portion of ultra-violet in sunlight does the job, known as UV-B. The wavelengths for UV-B range from 280 to 315 nanometres, and vitamin D is best-produced by light in the range 295 to 297 nanometres.
Exposing most of your skin to strong sunlight for about 20 minutes can produce between 10,000 and 20,000 IU of vitamin D3, if you skin is fair. That’s about twice as much as you need per day, on average. (If you are dark-skinned you might take an hour or more to produce the same amount.)
As our ancestors moved further away from the equator, less sunlight was available – especially during winter. So food became an important secondary source of vitamin D, tiding them over the colder months.
Vegetable Sources of Vitamin D
Vitamin D food sources can be either vegetable or animal.
Vegetable sources are mainly
- algae (which most people don’t eat, but it gets into the food chain through fish)
Wild mushrooms can produce quite substantial amounts of vitamin D2 (ergocalciferol) if they have been exposed to strong sunlight.
Commercial mushrooms are grown indoors and not subjected to UVB light. Therefore they contain no vitamin D. However, it is worth knowing that if you irradiate cultivated mushrooms that you buy at a store, by placing them in strong sunlight for half an hour or so, you can produce around 1500 IU of vitamin D2 per medium-sized punnet.
So this kind of vitamin D can occur naturally in our diet. We can use it, but it’s not the ideal form for us. Our bodies are optimized for vitamin D3, the kind our skin produces.
But getting all your vitamin D as vegetable-sourced vitamin D2 would be much, much better than getting no vitamin D at all.
Vitamin D from Fortified Foods
Most people who live in first-world countries get some vitamin D from fortified foods, including
|Some Orange Juices||Cup||100|
|Some Breakfast Cereals||3 oz||Small amount|
This is not nearly enough to prevent vitamin D deficiency.
These are average values. In practice the level of fortification in foods varies. Another concern is that some fortification programs use vitamin D2 instead of vitamin D3. (If foods don’t specifically state vitamin D3, assume they contain vitamin D2)
Animal Sources of Vitamin D3
|Salmon||3 oz||180 - 500|
|Mackerel||3 oz||80 - 290|
|Sardines||3 oz||80 - 400|
|Tuna||3 oz||50 - 600|
|Egg Yolks||1 Yolk||25|
|Liver (beef)||3 oz||13|
|Cod Liver Oil||1 tsp||500|
Animals use vitamin D just as we do, and we can obtain it from them, in the form of vitamin D3.
As you see, it is possible to obtain meaningful amounts of vitamin D3 from our diet, but only if we eat a great deal of fish!
Depending on where our fish is caught, so much fish may not be good for us, because of the pollution of our oceans (with PCBs and heavy metals).
And please don’t ask me how fish convert the vitamin D2 from the algae they eat into vitamin D3. I don’t think anyone knows how they do it.
In practice, the average daily vitamin D intake (D2 and D3) from food is probably less than 200 IU per day for most people, which is far less than we need.
Cod liver oil as a source of vitamin D3
Natural cod liver oil contains about 5000 IU of vitamin A, but only 500 IU of vitamin D per teaspoon.
If you were to drink several teaspoons a day (not recommended), the vitamin A would reach toxic levels before you got enough vitamin D.
Some cod liver oils are processed to remove the natural vitamins. Then after processing, synthetic vitamin A and vitamin D2 are added back into the oil. The natural proportions of vitamin A to vitamin D may also be changed in such oils.
Cod liver oil seems like a great way to get your omega-3 fatty acids at the same time as your A and D vitamins, but in fact you cannot get enough vitamin D from natural cod liver oil alone without getting an overdose of vitamin A.
Also, vitamin A may compete for absorption with vitamin D, so if you are trying to raise your vitamin D levels, taking extra vitamin A (retinol) could be counter-productive.
Vitamin D Supplements
The easiest and perhaps safest way to increase your vitamin D level is to use vitamin D3 (cholecalciferol) supplements. Supplements of vitamin D2 (ergocalciferol) are also available, but are probably less effective.
Vitamin D3 supplements are widely available in most countries. In most first-world countries you can now obtain vitamin D3 in capsule sizes ranging from 400 IU to 10,000 IU, or even 50,000 IU.
Sadly, some countries restrict the maximum vitamin D capsule size to 400 IU or 1000 IU. This makes it harder, and more expensive to take an effective dose. But even in those countries, you can usually order vitamin D online.
Tanning Beds and Sunlamps
One last alternative, for people with deep pockets – you can use a safe tanning bed to provide UV-B to your skin all year round, in precisely controlled doses.
UV lamps are also available to do the same thing.
The equipment has to provide exactly the right wavelengths of UV light, in the right proportions, in order to be safe. Buy from a reputable manufacturer, and use strictly in accordance with their instructions.
So What is the Best Source of Vitamin D?
Now you know what your options are for getting the vitamin D your body needs. Most people should concentrate on sunlight and supplementation, which is not to discourage you from eating fish!
Fish – from unpolluted waters – is a very healthy food, but it can only go so far in meeting your vitamin D needs, unless it forms a very large part of your diet.
Both sunlight and supplementation need to be used with care and understanding, for different reasons.
- Sunlight can damage your skin if you take too much at one time. See Safe Vitamin D from Sunlight.
- Vitamin D Supplements must be taken in appropriate doses, which are not the same for everyone.
Finally, when increasing your level of vitamin D to near-optimum, it is important that other nutrients are also taken in the right quantities, particularly calcium, magnesium, vitamin K and vitamin A. See Vitamin D Co-Factors.