It’s hard to get enough vitamin D through diet alone. Most people get vitamin D from exposing their skin to sunlight but getting enough vitamin D even from sunlight is a challenge if you live in Northern latitudes where the sun is weaker or you spend all day indoors.
Most people need 15 minutes of sun exposure most days of the week to synthesize enough vitamin D for health, and darker skin people and those who are overweight need even more. That’s why more people are taking a vitamin D supplement these days. However, it’s best to discuss this with your doctor first since it’s possible to get too much vitamin D through supplementation.
What if your doctor checks your blood level of vitamin D and tells you it’s too low? They might recommend that you take a vitamin D supplement and tell you how much to take. Here’s the kicker. How you take that vitamin D will determine how much you absorb and how much benefit you will get. It might tempt you to take your vitamin D supplement with a cup of coffee in the morning on an empty stomach. Unfortunately, you won’t get the full benefits if you take it this way.
Why is it better not to take vitamin D on an empty stomach? Your body needs a source of fat to optimize absorption of this fat-soluble vitamin. Studies show that you absorb vitamin D best when you take it with a meal that contains modest amounts of fat. So, you wouldn’t take it on an empty stomach or with a meal that contains little or no fat, at least if you want the full benefits.
On the other hand, too much fat can hinder vitamin D absorption too. In one study, taking a vitamin D supplement with 11 grams of fat boosted vitamin D absorption more than taking it with 35 grams of fat. Therefore, you need some fat but not too much for your body to take up the most vitamin D from a supplement. If you don’t consume some fat, you’ll absorb about 30% less vitamin D from a vitamin D supplement. The optimal amount of fat, based on limited studies, is around 11 grams.
What Happens if You Get Too Much Vitamin D?
Vitamin D toxicity is uncommon. It’s more common that people are deficient in the “sunshine vitamin.” However, if you were to take large doses of a vitamin D supplement, it could be harmful. When you get too much in supplement form, you absorb more calcium from your digestive tract. This can lead to an elevated blood level of calcium and a build-up of calcium in your urine. When calcium accumulates in the urine, it increases the risk of kidney stones. In the blood, it can lead to muscle weakness, digestive upset, nausea, mental status changes, and dehydration.
Over a long period, taking too much vitamin D could cause calcium to build up in the inner walls of arteries and tissues throughout the body. If it builds up in the arteries, it can lead to irregular heart rhythms or even death. Taking large quantities of vitamin D can also lead to kidney failure. However, this is uncommon and occurs when people take far above the recommended dosage for a long period of time.
The risk of toxicity is only a problem if you take a vitamin D supplement. When you get your vitamin D from sun exposure, your body has ways of self-regulating how much vitamin D you form. However, the more concentrated ultraviolet light you get from tanning beds can cause a significant rise in vitamin D, enough to be toxic.
Do You Need a Supplement?
The best way to know whether you need a vitamin D supplement is to check a level. If you’re young, lean, and spend a lot of time in the sun, you may meet your vitamin D requirements through lifestyle alone. But if you’re in one of these higher-risk groups, see where you stand, so you’ll know whether you need a supplement and how much you should take. These are signs risk factors for vitamin D deficiency:
- Having darker skin
- Spending little time in the sun
- Living in a Northern climate
- Being overweight or obese
- Being over the age of 50
- Wearing sunscreen most of the time
- Having certain medical conditions such conditions involving the digestive tract, kidney disease, or liver disease
If you take a vitamin D supplement, don’t take over 4,000 I.U. per day unless you’re under the care of a physician who is monitoring your levels, and most experts don’t recommend taking more than 2,000 I.U. daily without close monitoring. Adults over the age of 19 should get at least 600 I.U. daily and adults over 70 need 800 I.U. each day. After the age of 70, the risk of deficiency is higher since people spend more time indoors and they have less ability to make vitamin D from sun exposure. For humans, vitamin D is the main source of vitamin D since few foods, other than fatty fish, fortified foods, and mushrooms exposed to ultraviolet light, contain vitamin D.
Some people cannot get enough vitamin D to avoid deficiency from sun exposure alone. If you have medical conditions that could affect your vitamin D level, talk to your physician about how much you should take.
The Bottom Line
You need vitamin D for good health, and if you take a vitamin D supplement, you need to absorb enough of it to get benefits. To do that, consume a vitamin D supplement with a food or snack that contains fat. The optimal amount of fat is around 11 grams. Too much fat may reduce absorption. Be sure you’re taking an appropriate dose too. There’s less room for error when you take a fat-soluble vitamin, like vitamin D, since your tissues store the excess.
- com. “Fat-Soluble Vitamins 101”
- J Bone Miner Res. 2013 Aug;28(8):1778-83. doi: 10.1002/jbmr.1896.
- J Acad Nutr Diet. 2015 Feb;115(2):225-30. doi: 10.1016/j.jand.2014.09.014. Epub 2014 Nov 17.
- National Institutes of Health. “Vitamin D”
- LeFevre ML. Screening for vitamin deficiency in adults: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2015;162:133-40.
- Holick MF. Vitamin D deficiency. N Engl J Med 2007;357:266-81.