Signs of Deficiency and How to Get More

I’m writing this from a coffee shop in Portland, Oregon, and it’s (shockingly!) raining as I type. If you’ve ever watched Portlandia or know anything about Portlandia, which, against all weather forecasts, is my favorite place in the country, this isn’t unusual. What’s unusual is that I’ve spent the better part of the last decade telling myself that four weeks of actual sunlight each summer is probably enough to keep my vitamin D levels at a decent level. Not so, dear reader.

based in brooklyn Maya Ferrer’s Nutrition and author eat from the rootsVitamin D deficiency is estimated to affect up to 75% of adults, and that number applies even to people who call themselves health-conscious, outdoorsy, and doing everything right. It’s easy to dismiss the signs of a lack of energy as something else entirely. Fatigue. I feel low. The common feeling of running on empty can be attributed to schedule, sleep, stress, and anything else other than the nutrients your body is supposed to make from sunlight.

We asked Mr. Ferrer to explain what’s really going on and what you can do about it.

Why is vitamin D deficiency so common?

The short answer is that the systems we rely on to produce vitamin D are more fragile than most people realize. “Vitamin D is synthesized subcutaneously through the skin,” Ferrer explains. “UVB rays from the sun trigger a reaction in which the skin produces vitamin D. However, depending on the amount of melanin in a person’s skin, this process can take anywhere from 5 to 30 minutes once the skin is exposed to the sun.”Additionally, most of us wear sunscreen, spend most of our daylight hours indoors, and live quite far from the equator, so UVB rays If we take into account the fact that the rays become weaker for several months at a time, the calculations begin to become unfavorable.

Food is not a reliable backup. Vitamin D occurs naturally in only a few foods, such as egg yolks, salmon, liver, and certain mushrooms, and fortified foods such as milk and cereals rarely contain enough amounts to be effective on their own. “These foods tend to be under-consumed and, as a result, do not have a significant effect on vitamin D levels,” Ferrer points out.

I’m sorry to write this, but some people start from a disadvantageous situation. Ferrer warns that several groups are at increased risk, including people with liver disease (because the liver is involved in the metabolism of vitamin D), people with gastrointestinal or malabsorption disorders, people with dark skin who live in northern regions or far from the equator, and people who spend a lot of time indoors. If you fall into more than one of these categories, or if you live somewhere that has reliably sunny skies for, say, four weeks a year, it’s worth paying attention to.

How do I know if my health is low?

The frustrating thing about vitamin D deficiency is that the symptoms are exactly what you’d expect. Ferrer cites increased susceptibility to disease as one of the most obvious signs. You need enough vitamin D to support immune function, so if you’re aware of everything going on around you, it’s worth noting. Feeling depressed and tired are also common indicators, especially those that are likely to be caused by anything other than nutritional deficiencies. People with low vitamin D levels are at higher risk for depression, and chronically low vitamin D levels can affect bone health for years before becoming apparent.

What vitamin D actually does (beyond bone health)

The benefit most people associate with vitamin D is bone health. And while that’s true, it’s not the most surprising thing on the list. What’s even more interesting is what’s happening elsewhere.

It’s the mood that makes it worth leading. “Decreased vitamin D levels are associated with increased symptoms of depression and anxiety,” Dr. Ferrer says. “It is thought that a deficiency may worsen symptoms.” Although this is an area where research is inconclusive and suggestive, and vitamin D is not a cure for depression, Ferrer believes the association is consistent enough that it’s worth discussing supplements that are safe for people managing anxiety or depression.

Beyond mood, adequate vitamin D supports immune function, regulates calcium absorption, and reduces inflammation. Research into the potential for broader disease prevention, including cardiovascular health, certain cancers, and cognitive function, is still evolving, and Ferrer is cautious about what the evidence is solid and what is exaggerated. Vitamin D is necessary, its deficiency has real secondary effects, and getting enough is a reasonable basic priority.

How to actually get more vitamin D

The three sources are the sun, food, and supplements, and they cannot be replaced. “Vitamin D processing depends on many factors, including the individual’s basic health and ability to absorb vitamin D from both food and supplements,” Ferrer explains. What works for one person may not work for another. This is part of the reason why deficiency persists even among people who think they have the basics covered.

solar

Most efficient source if available. According to harvard healththe general guidance is:

• Ideally, give your arms and legs about 10 to 15 minutes of direct sunlight, around midday when UVB rays are strongest.
• Skip SPF on that window. Sunscreen blocks UVB rays and significantly reduces vitamin D synthesis.

food

For those who eat animal products, Ferrer recommends egg, salmon, liver, and fish liver oils as a starting point. “People can safely consume one egg a day, seafood twice a week, and two ounces of liver weekly as functional therapies,” she says. For those who eat a plant-based diet, the options are even more limited.

• Mushrooms exposed to ultraviolet light are an outstanding natural source
• Fortified plant milks and cereals are complementary options, but they rarely correct deficiencies on their own.

supplement

This is where most people end up and where the most common mistakes occur. Mr. Ferrer’s guidance:

• Don’t take supplements without knowing your baseline levels first
• Follow up on lab work to ensure your plan is working
• Look for D3 (cholecalciferol) over D2. This is the form that your body naturally produces and absorbs more efficiently.
• It’s worth checking to see if a third-party quality seal (USP, NSF, or Informed Sport) is affixed to the label.

Notes on testing and dosage

If the symptoms look familiar, testing is easy. “Clinical tests are mostly accurate and very reliable,” Ferrer says. Ask your doctor to include a vitamin D test in your next annual blood test. This is a simple addition and most insurances will cover it. Knowing your baseline will completely change the way you approach supplements.

According to NIH Office of Dietary Supplementsthe recommended daily intake is 600 IU for most adults up to age 70 and 800 IU for those over 70, and higher amounts may be recommended for those managing a deficiency. However, since vitamin D is fat-soluble and accumulates in the body, more is not necessarily better. Your health care provider can help you find the right number for your particular level and situation.

takeout

Vitamin D is not a health trend. This is not a fad supplement or a nutrient rebranded for a new audience. This is the foundational, supporting system that works in the background and improves everything else. Getting enough of it is one of the small adjustments you can make to get longer profits. Even if you live somewhere, it’s raining right now as I type.

This post was last updated on June 30, 2026 with new insights..