While caffeine-filled beverages like lattes, flat whites, and cold brew offer plenty of potent health benefits, medical researchers in China and Brazil have found one more reason why it’s nevertheless important to consume caffeine in moderation. When consumed in excess, caffeine can impact your body’s ability to absorb vitamin D.

The new cross-sectional study published in the International Journal for Vitamin and Nutrition Research looked at data collected from a 2005-2006 National Health and Nutrition Examination Survey on vitamin D levels and dietary caffeine intake from 13,134 individuals (aged 30-47 years old). Their findings show that higher intake of caffeine was associated with poor vitamin D absorption in what they call “a representative sample of the American population” after adjusting for various health-related variables.

But before you consider tossing your morning brew, it’s important to mention that the study’s authors clearly state that further investigation is required to determine whether caffeine actually causes vitamin D deficiency. Additionally, it’s unclear what they determine is a healthy versus an unhealthy amount of caffeine intake; after all, everyone’s body responds drastically differently to caffeine. According to integrative medicine doctor Erica Schwartz, MD, up to 400 milligrams of caffeine per day—about four or five eight-ounce cups of coffee or two energy drinks—is considered safe for most adults. But again, keep in mind that caffeine tolerance varies greatly between individuals.

While monitoring your caffeine intake is vital, it’s equally important that this study’s findings inspire you to take a look at how much vitamin D you should be getting, symptoms of vitamin D deficiency to keep an eye on, and the best foods that will help you up your vitamin D intake.

Can we get all the vitamin D we need from the sun?

In the U.S., the recommended dietary allowance (R.D.A.) of vitamin D is 600 IU for everyone, including those who are pregnant or breastfeeding, between the ages of one and 70. People over the age of 70 are typically recommended to get 800 IU to account for decreased vitamin D absorption and increased risk of bone fracture.

Vitamin D is known as the “sunshine vitamin” because it can be made in the body through exposure to sunlight. “In general, twenty to thirty minutes of mid-day exposure to sunlight on a large portion of exposed skin can produce about 10,000 to 20,000 IU,” says Michael T. Murray, ND, author and chief scientific advisor at iHerb. “In light skinned individuals exposing much of their body to direct sunlight might produce as much as 10,000 IU in 10 minutes; in darker skinned people it may take considerably longer sun exposure to produce the same amount.”

But skin color isn’t the only barrier that can limit the efficacy of sun exposure to get your body to produce vitamin D. “Although your skin manufactures vitamin D when exposed to the sun, the process isn’t always efficient,” says Samantha Cassetty, MS, RD and advisor to Performance Kitchen. “For instance, if you’re wearing sun protection or it’s cloudy, the activation process is less effective. Plus, the risks of sun exposure, like skin cancer, outweigh the benefits of vitamin D activation, so it’s better to focus on food and supplements than spending time in the sun without adequate sun protection.”

What are the best vitamin D foods?

Unfortunately, vitamin D isn’t naturally found in many foods. “Foods that contain higher amounts of vitamin D include mushrooms, fatty fish, fish liver oil, and eggs, but many foods and beverages like milk, orange juice, and cereal are fortified with vitamin D,” says Valerie Agyeman, RD, LDN and Nature Made wellness ambassador.

In terms of getting the most vitamin D bang-for-your-buck, Cassetty says that salmon is probably the top source of vitamin D. “A three-ounce serving of cooked, farmed Atlantic salmon supplies about 450 IUs of this nutrient. Plus, you’ll get much-needed omega-3 fatty acids as well as a quality source of protein,” she says. Cassetty highlights other options below:

• Two eggs have 82 IUs, which is concentrated in the yolk. Eggs are also an easy source of protein.
• A tin of sardines provides 178 IUs of vitamin D, as well as omega-3 fatty acids. Sardines can be somewhat polarizing, but if you like them, they’re extremely nutritious.
• A cup of milk has 117 IU, since milk is traditionally fortified with vitamin D. So, if you’re using a dairy alternative, it’s a good idea to check labels to find a substitute that’s fortified with vitamin D as well as calcium. You’d be surprised by how many dairy-free milk products aren’t fortified.
• 1/2 cup raw mushrooms provides 366 IU.
• Sometimes cereal is fortified with vitamin D, and if this is the case, you can meet about 15 percent of your daily needs between a serving of cereal and a half cup of milk.

According to Murray, however, dietary sources of vitamin D are insufficient in most circumstances to meet requirements. “Most health experts are recommending supplementation with a dosage of vitamin D3 in the range of 2,000 to 5,000 IU daily. The only way to determine where a person may fall is by testing. Many doctors are now routinely checking vitamin D status in their patients.” Murray also says that taking vitamin D3 with a meal containing some fats or oils will enhance the absorption. Keep in mind that, while vitamin D and D3 are often considered interchangeable, in terms of supplements, vitamin D3 is slightly easier to absorb.

How your body is telling you it needs more vitamin D

If you’re a six-cups-of-coffee-a-day kind of person, some signs of vitamin D deficiency to look out for, according to Agyeman, are muscle weakness, hair loss, reduced immunity, fatigue, and bone loss and/or pain.

“Since vitamin D is involved in promoting calcium absorption, inadequate intake may result in thin, weak bones, which may ultimately lead to osteoporosis,” says Cassetty. “Plus, it’s involved in regulating inflammation in our immune response, which may be why low levels are linked to higher rates of viruses and autoimmune disorders. Vitamin D deficiency has also been linked to type 2 diabetes. You might experience vague symptoms, like fatigue, or you might not have any symptoms. That’s why it’s smart to get your levels checked periodically and to take a supplement.”

Vitamin D aside, it’s wise to consider consuming caffeine in moderation.

“Regardless of your source of caffeine, many health organizations recommend restricting it to 400 milligrams per day for healthy adults,” says Agyeman. As mentioned, that’s about four to five small cups of black coffee. “Pregnant women, breastfeeding women, individuals with hypertension, and the elderly should consider limiting their intake due to increased risk of negative side effects from caffeine such as anxiety, heart palpitations, and headaches. Children and teens should also limit total caffeine intake as it may raise blood pressure and lead to sleep disruptions,” she says.

Bottom line? It may be time to consider turning your double espresso into a cappuccino made with fortified milk.

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