Live above this line? You may need a vitamin D supplement

last updated: Nov 19, 2019

5 min read

Some of us just get the short end of the nutrient stick, thanks to biology. Women need more iron than men, for example. Vitamin D is one of those nutrients.

Although we could all stand to do better about boosting our intake, some people at simply at a higher risk for deficiency because they have darker skin. Though 41.6% of adults in the United States don’t get enough, that number surged to 82.1% and 69.2% of African Americans and Hispanics, respectively (Forrest, 2011).

But another factor that increases your need for this “sunshine vitamin” is one you may not have considered: geography.

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What is vitamin D?

Vitamin D (calciferol) is actually a group of steroids that act like hormones in the body. Humans need two main essential forms: vitamin D2 (ergocalciferol) and D3 (cholecalciferol), both of which offer the same health benefits, though D3 may be better absorbed and, therefore, more effective as a supplement (Tripkovic, 2012).

As a fat-soluble vitamin, the Ds are stored in your body’s fat tissue, and they require some fat in your diet in order to be absorbed. It’s called the sunshine vitamin for a reason: our bodies produce the Ds through sun exposure thanks to UVB rays.

But legitimate concerns about skin cancer mean increasing your dietary intake, and taking vitamin D supplements, are likely the safest options for preventing deficiency. There’s simply no amount of “safe” sun that can be prescribed without sunscreen.

Vitamin D’s role in the body

Vitamin D is vital enough to your body that the health benefits of getting enough ripple out across all your major systems.

It can decrease your risk of catching the flu, alleviate symptoms of depression, and reduce risks associated with high blood pressure during pregnancy. Low blood levels have been associated with increased risk of cardiovascular disease, asthma in children, and cognitive impairment in older adults (Martineau, 2017; Sasan, 2017).

The Ds are also essential for bone health, critical cellular functions from cell growth to death, and potentially even diabetic health.

What happens when you don’t get enough

If you don’t have sufficient vitamin D, you might encounter a myriad of health issues from respiratory problems and hair loss to bone loss, infertility, and weight gain (LeBlanc, 2012).

Deficiency is when your levels fall below 12 ng/mL. Everyone is different, so you may have only a couple of these symptoms, or your experience may differ completely. Either way, your healthcare provider will need to run blood tests to diagnose a deficiency and begin to treat it through diet changes and even supplementation.

People with gastrointestinal diseases such as Crohn’s disease and celiacs may even need additional supplementation since they can have trouble absorbing the vitamin.

Vitamin D deficiency and geography

By now, it should be clear that none of us can afford to ignore our vitamin D status. But even if you’re free of gastrointestinal diseases, have no problems with malabsorption of nutrients, and don’t have darker skin, you’re not in the clear.

UV levels are the highest in the summer, which means even if you spend time outside during the other seasons, you’ll be producing less vitamin D (again, we cannot advise any time in the sun without the protection of sunscreen). Past studies have been mixed about the effect of latitude on vitamin D and also whether it was a significant risk factor for a deficiency when compared to other factors.

A study from 2017 wanted to get to the bottom of these differences by testing them within the United States. They used medical students based in Florida and Pennsylvania as test subjects.

Researchers found that 5% of participants based in Florida were deficient, compared to 13% of those based in Pennsylvania. Even after controlling for other factors, the Florida participants had higher average vitamin D levels than their northern neighbors (Leary, 2017).

But it turns out we can get more granular than this. Researchers have pinpointed the exact longitudinal line (geographical lines that run around the width of the globe on maps) above which they believe people might need more vitamin D.

In the United States, that’s anyone above 37 degrees North, an imaginary line that starts in southern Virginia and runs on the northern border of Oklahoma through central California (Holick, 2006).

But we still don’t have it quite figured out

Not all researchers agree with this line, however, or the idea that latitude even has a big enough impact on vitamin D production to cause concern. A 2009 survey of 394 past studies found no link between vitamin D levels and latitude (Hagenau, 2009).

Unadjusted, the numbers did show a decrease in vitamin D status the further South a person lived––but only in Caucasians. Once the data was controlled for age, gender, and ethnicity, that correlation disappeared.

Regardless of where you live, other factors are likely to play a larger role in determining your vitamin D status. A 2007 study by researchers in Australia found that only around 4% of the variation in vitamin D levels was due to latitude (van der Mei, 2007).

What season it was played a bigger role, around 14%. That’s good news—you don’t need to move south just to get enough vitamin D. You might just need to take a closer look at what lifestyle choices you’re making.

Getting a proper diet, which can include vitamin D supplements, can ensure that your vitamin D levels are healthy even if you live in sun-starved areas of the world.

Dangers of a long-term deficiency

Since even low levels of vitamin D are associated with unpleasant side effects, a true deficiency shouldn’t be taken lightly.

Although every person reacts differently, symptoms of vitamin D deficiency may include nonspecific signs such as muscle weakness and fatigue, physical problems ranging from inability to heal wounds to respiratory issues, and even mental health issues such as anxiety and depression.Long-term deficiency is extremely dangerous. Since the vitamin plays an integral role in calcium absorption and bone health, an ongoing deficiency could lead to serious conditions, such as rickets or osteomalacia.

Although rickets is more common in children and osteomalacia in older adults, both are characterized by a weakness of the bones. In the case of rickets, this can lead to bow legs; osteomalacia increases the odds of bones breaking due to decreased mineralization.

To avoid deficiency, the National Academy of Medicine recommends that people up to the age of 70 get 600 IU (15 mcg) of vitamin D per day. Older adults above 70 should get 800 IU (20 mcg) per day (Inst. of Med, n.d.).

How to get more vitamin D

Since there’s no safe recommendation that can be made for spending time exposed to UV light without sunscreen, your best bet for upping your vitamin D status are lifestyle changes that incorporate more dietary sources and supplements.

Vitamin D-rich foods aren’t difficult to come by, but the very best sources may not suit everyone: we’re talking about cod liver oil, oily fish such as sockeye salmon or mackerel or herring, and beef liver. If none of those sound good to you, egg yolks also boast the vital nutrient. For vegetarians and vegans, there are limited natural sources, like mushrooms, but plenty of fortified foods that can bring up their dietary intake. Foods with added vitamin D include some breakfast cereals, orange juice, and soy milk.

You just need to check that you’re buying the fortified version. Lacto-ovo vegetarians have an easier time since they can also get vitamin D through fortified dairy, such as milk and cheese.But supplements are also widely available. But although vitamin D2 and D3 provide the same benefits, D3 may be better absorbed than D2, so you might want to grab one of these supplements if available. Many D3 supplements, however, are made by exposing lanolin from sheep’s wool to UVB rays, so it is not vegan-friendly.

The most important factor in getting enough of the sunshine vitamin is that you take the supplement consistently, so if you need to take D2 because of dietary restrictions, that’s OK.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

November 19, 2019

Written by

Linnea Zielinski

Fact checked by

Jefferson Chen, MD