by Lauren Panoff, MPH, RD, DipACLM
People often assume vitamins are a single category of nutrients, but the fat-soluble vitamins—including A and D—play distinct and connected roles in your body. Understanding their differences and purposes can help you make smart nutrition and supplementation choices.
Vitamin A is a nutrient your body cannot make on its own, so you have to get it from your diet or supplement routine. You might be surprised to learn that vitamin A isn’t actually one nutrient, but a group of related molecules found in two forms, depending on their source:
The fat-soluble nature of vitamin A means that it’s not excreted from your body the way that water-soluble vitamin C and the B vitamins are. Instead, it’s absorbed with the fats you eat and stored in your liver. Your body can pull from these reserves, but excessive intake can lead to toxic levels.
Vitamin A has several important jobs:
Vitamin D technically behaves more like a hormone than a vitamin in your body and is involved in nearly every system.
Unlike vitamin A, vitamin D can be made by your body. The process is triggered when your skin is exposed to ultraviolet B (UVB) rays from the sun. Still, factors like age, where you live, time of year, and skin pigmentation can affect how much vitamin D is produced this way.
There are two forms of vitamin D:
Vitamin D receptors are found in nearly every cell and tissue in your body because this nutrient is involved in things like:
Vitamins A and D interact, influence each other's activity, and in several key areas, work together to produce health effects that neither could have alone.
First, both are needed for a healthy immune system, but they contribute in complementary ways. Vitamin A maintains the physical barriers (the linings of your gut, lungs, and skin) and supports immune cell production. Vitamin D helps coordinate and manage your immune response once it's underway.*
Additionally, when either nutrient is present in very large amounts, it can interfere with the other nutrient's signaling. Overall, more isn’t always better, and it’s important to find a balance of both.
Vitamins A and D are found in a variety of foods, but not everyone meets their needs through diet alone, and supplements can be helpful.
Retinol is found in animal foods like:
Beta carotene is found in plant foods like:
Vitamin D is found naturally in certain fatty fish (salmon, mackerel, herring, sardines), cod liver oil, egg yolks, beef liver, and mushrooms exposed to UVB. It’s also added to certain foods like fortified milk and plant milk, OJ, and cereals.
When supplementation makes sense, Puritan’s Pride has you covered with a line of vitamin A and D, including D3 easy-to-swallow softgels, liquid vitamin D3, and vitamin D gummies. Our beta-carotene supplement provides 7,500 mcg of vitamin A per serving.
The established recommendations for these nutrients are below. Vitamin A is expressed in Retinol Activity Equivalents (RAE), a unit that accounts for the difference in potency between preformed retinol and beta-carotene. Vitamin D needs are expressed in International Units (IU) or micrograms.
Vitamin A daily needs:
Vitamin D daily needs:
Not everyone needs a supplement. The best way to know your vitamin D status is to have your blood tested for 25-hydroxyvitamin D, the storage form of vitamin D that reflects dietary intake and sun exposure over previous weeks and months. This can help your clinician determine whether low levels need attention or if a supplemental maintenance dose is adequate.
Vitamin A blood testing is less routinely ordered, but can be done through a serum retinol test at the discretion of your healthcare provider.
Vitamins A and D have important jobs in your body, but they’re also two commonly under-consumed nutrients. It’s not because people aren't trying to eat well, but because the realities of modern life can make it harder to prioritize. Fortunately, diet changes and appropriate supplementation can help.
Check out our line of vitamin A and D supplements to find one that best suits your needs.
*These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
