Like other vitamins, vitamin D is a substance needed for health but only in tiny amounts. Unlike other vitamins, it doesn't occur naturally in food but can be made in the body. Most people know that humans use sunlight to make vitamin D, the "sunshine vitamin." But modern humans don't get much sunlight, so we end up at the vitamin counter, often confused about what to buy.
Our bodies make vitamin D3, cholecalciferol. At the supplement counter, you can choose from D3 or D2. Vitamin D2 is ergocalciferol, which differs slightly from D3 but behaves the same way in the body. D3 is slightly more potent.
The main difference between the two supplements is how they are made. D3 comes from animal sources, although it can be made from lichen. D2 is derived from plant sources. If you are a vegan or vegetarian, you'll want to read labels closely.
Vitamin D is fat-soluble (absorbed along with fats), but taking it with oily foods isn't necessary. You can also get vitamin D from food. In the United States, many foods such as soy, almond, and oat milk are fortified with vitamin D. Few foods in their natural state contain vitamin D.
Why You Need Vitamin D3
Authorities disagree about how much vitamin D the body needs. In the United States, the Daily Value (DV) for vitamin D has been set at 800 International Units (IU).
A deficiency of vitamin D can have serious consequences in the body. Vitamin D is vital for these reasons:
1. Bone Health
Doctors discovered vitamin D when they were studying rickets, a children's bone disorder. Today rickets is rare, but vitamin D is still needed for bone health. It's especially important for women past menopause, who are at risk of osteoporosis. Vitamin D is also used to treat a more serious bone condition called osteomalacia (softening of bones). Vitamin D allows the body to absorb calcium. Without vitamin D, the body uses only a small percentage of the calcium in food.
2. Anti-Cancer Properties
Higher levels of vitamin D in the blood are associated with lower levels of some cancers, including colorectal, prostate, and pancreatic. In animal studies, vitamin D was associated with fewer tumors and slower growth of tumors. Clinical trials in humans suggest that vitamin D may not prevent cancer but may slow its progress.
3. Brain Health
Low levels of vitamin D may be a risk factor for various forms of dementia, including Alzheimer's disease. Animal studies and cell studies have shown a connection, but the results of clinical trials have been mixed. Further research is needed.
Foods with Vitamin D
Remember that you have three choices about how to get your vitamin D:
- Your diet
Doctors often favor the supplement because of the dangers of UV rays and the difficulty of getting vitamin D from diet alone. Oily fish is the best source of D3, but few people want to eat fish daily.
In the United States, these foods are usually fortified with vitamin D2:
- Cow's milk
- Plant-based milk
- Infant formula
- Breakfast cereal
- Orange juice
Remember that Vitamin D2 is found mainly in plants, while D3 comes mainly from animals. Mushrooms, especially when exposed to UV light, are a rich source of vitamin D, but it is mostly D2 with some D3.
When listing the amount of vitamin D in foods, most sources do not distinguish between vitamin D2 and D3. Some foods will contain a mixture of both forms. The following foods are rich in vitamin D, and since they are animal sources, they contain mainly D3:
1. Rainbow trout, farmed
Just 3 ounces of rainbow trout provides 645 IU for 81% of the DV. It is also rich in heart-healthy omega-3 fatty acids.
2. Sockeye salmon
Sockeye salmon has slightly less than trout at 570 IU and 71% of the DV. Salmon can contain mercury, but some authorities say the benefits of salmon outweigh the hazards, especially when eaten in moderation.
A typical serving of sardines, which is about one can, would provide around 200 IU. Sardines offer other nutrients, such as vitamin B12 and omega-3s.
With 44 IU and 6% of the DV, the vitamin D in one egg is almost identical to two sardines. The cholesterol content makes loading up on eggs inadvisable.
5. Beef liver
Some people love liver. Some people hate it, but it packs a nutritional punch, with lots of protein, iron, and vitamin A. Like eggs, it is quite high in cholesterol. The vitamin D in 3 ounces of liver is 42 IU for 5% of the DV.