Vitamin D: How to get enough without the sun

by Kaetlin Zink

Our bodies can naturally convert just ten to fifteen minutes of sunlight exposure into large amounts of vitamin D. As we transition into the fall and winter months, however, we start to lose this major source of the vitamin, potentially leading to deficiencies.

According to the CDC, upwards of 30% of children and adults in the US are vitamin D deficient. What’s more, the Endocrine Society has found that levels may fall as much as 50% in the winter.

Why is Vitamin D so important?

According to the National Institutes of Health, not only does Vitamin D play a crucial role in calcium digestion and bone health, but it also aids in the proper functioning of the immune system and other important organ systems. Because the vitamin controls the expression of genes signaling your immune system to attack and destroy viruses and bacteria, it also helps combat all kinds of infections.

Vitamin D even plays a crucial role in maintaining cell growth and fighting off cancer, as there is strong evidence suggesting higher intakes of the vitamin decrease the threat of colorectal, prostate, and other detrimental cancers by 30 to 50%.

Being deficient in vitamin D for a prolonged period can even cause many negative health effects, including autoimmune system issues (anything that prevents your body from properly fighting off and preventing illnesses and other health problems, such as inflammatory bowel disease and multiple sclerosis), cardiovascular disease or other heart complications like heart attack or stroke, infections like influenza, problems with DNA repair and metabolic processes, Alzheimer’s disease, diabetes, osteoporosis, and more.

During the colder months, spending more time indoors can mean we lose our key source of vitamin D — the sun. People who work a 9-5 office job are more prone to deficiency.

Deficiencies & Daily Recommendations

Before the year 2000, very few doctors even contemplated the plausibility of being Vitamin D deficient. With the advent of increasingly more available and inexpensive technology to test for deficiencies, however, more and more studies began highlighting this previously overlooked issue.

In fact, according to the Insitute of Medicine, as of 2010, the RDA (Recommended Daily Allowance) for the majority of children and adults has risen from 200 IU per day to 600 IU per day. They also doubled the safe upper limit from 2,000 IU to 4,000 IU.

The RDA is the daily dietary intake level of a nutrient deemed adequate by the Food and Nutrition Board, meeting the requirements of 97.5% of healthy individuals regardless of gender or life-stage. It is calculated based off the EAR (Estimated Average Requirements) and is typically 20% higher than the EAR, which is intended to satisfy the needs of 50% of those in a specific age group based off of a review of scientific findings.

While many adults are at risk for being deficient, some are more vulnerable than others. For example, those with breast cancer, prostate cancer, or other serious health conditions that exhibit low levels of Vitamin D may suffer fewer chances of survival than those who exhibit normal levels.

Vegetarians may be at a higher risk of vitamin D deficiency because most foods rich in vitamin D are animal based. 

The National Institutes of Health also found that people who work in a standard nine to five office job are more prone to deficiency, as they likely are not gaining enough sunlight exposure. Others at risk, according to Prevention, include adults over the age of 55, people with a darker complexion, those with health conditions like inflammatory bowel disease and Crohn’s disease, vegetarians (most foods vitamin D-rich are animal-based), overweight people, etc.

According to the Endocrine Society, blood levels of vitamin D below 20 ng/mL is considered blatantly deficient, 21-29 ng/mL is considered insufficient, and 30-100 ng/mL is sufficient for optimal health.

Food Sources of Vitamin D

A great way to prevent deficiencies with depleted sunlight in the winter is by eating foods that are rich in Vitamin D, like these and more from Reader’s Digest:

  1. Salmon: With over 100 IU in just a single ounce, eat salmon for the best source of vitamin D. For a more cost-effective option, try canned salmon. Six ounces contains 323% of your daily need.
  2. Oysters: Half a dozen contains over 60% of your daily need.


  1. Shrimp: Six ounces has 64% of your daily value.
  2. Halibut: Three ounces has 254% of the recommended daily amount.
  3. Cod: Six ounces is equivalent to 18% of your daily value.


  1. Eggs: One large egg constitutes 4% of your daily value, but the yolk must be included.
  2. Cheese: One ounce of swiss equals 3% of daily need; one ounce of cheddar makes up 1%; one ounce of parmesan makes up 2%.
  3. Fortified products: Fortified milk, soy milk, tofu, juice, cereal, yogurt, and others provide additional sources of the vitamin.

How do you know if you’re deficient?

Here are some symptoms of deficiency to keep in mind during your annual checkup at the doctor (remember, these are not definitive):

  • Fatigue
  • Depression
  • Aching/sore bones
  • Trouble sleeping
  • Susceptibility to stress fractures
  • Poor athletic performance
  • Perspiration of the forehead
  • Weakened immune system
  • Erectile dysfunction
Be sure to know your levels and get them checked routinely. 

Be an advocate for yourself — know your ranges

If you aren’t soaking up enough sunlight for conversion, or aren’t too fond of seafood and other foods rich in Vitamin D or calcium — another great source for strong bones — it may be a wise idea to check your Vitamin D levels at the doctor during your annual checkup. If levels are found too low after administering a blood test, supplementation may be necessary.

As we delve further into fall and winter, it is important to be on the lookout for vitamin D deficiencies, especially if you’d consider yourself a sun worshipper. Remember, the best way to maintain healthy levels is by taking a blood test annually and by consulting your health care provider about any possible supplementation.


Hockessin Athletic Club opened its doors on June 10 2007. Boasting over 100,000 sq. ft., a 5-pool aquatics complex, and over 200+ weekly group and aqua fitness classes, it is Delaware's premier fitness destination. 100 Fitness Way, Hockessin, DE ·

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