Vitamin D is an often underrated, overlooked nutrient, though it should be held with high regard. This especially serves true in the winter months.
Maintaining adequate vitamin D levels in the winter months becomes even more important because many people “consume” or obtain their vitamin D from none other than the sun! And, in fact, 90 to 100 percent vitamin D requirement comes from sunlight exposure.
So, do you really need to take vitamin D in the winter? Find out the importance of vitamin D and how to maintain normal vitamin D levels year round.
What Is Vitamin D?
Vitamin D is critically important for the development, growth, and maintenance of skeletal structure. The vitamin is also an essential nutrient for healthy hair.
Vitamin D is mostly known for maintaining calcium homeostasis by helping the intestines absorb more calcium. Basically, when the body senses low calcium levels, it sends a signal for vitamin D to dissolve calcium from the bones and release it into the bloodstream.
Thus, calcium and vitamin D have a synergistic relationship that especially requires sufficient levels of vitamin D in order to function optimally.
Where Does Vitamin D Come From?
As mentioned, vitamin D comes from the biggest star in the sky. The epidermis and dermis, fancy terms for layers of skin absorb radioactive wavelengths of an inactive form of vitamin D. Once absorbed, the body works on converting it to an active form of vitamin D.
However, everyone’s ability to convert and absorb vitamin D is different depending on many factors like one’s skin pigmentation, sun protection with sunscreen and layers, one’s residence, and the season! Since vitamin D is derived from sun exposure, people tend to get less of it in the colder months. The time of day, latitude, and altitude can also affect vitamin D absorption.
Many resources suggest 10 to 30 minutes of midday sunlight is sufficient enough to reap the full benefits and naturally obtain enough vitamin D.
Foods High in Vitamin D
Some foods also contain vitamin D as well. From the months of October to about March, it is imperative to consume foods high in vitamin D, as the sunlight and amount of time spent in the sun is not sufficient to supply enough.
The best sources of vitamin D include:
- Oily fish like salmon, sardines, and herring
- Red meat
- Liver
- Egg yolks
- Fortified foods like cereals, orange juice, and some fat spreads (although these options lack other nutrients and can provide many empty calories)
- Milk and other dairy products sourced from certain places (NOT from the UK)
Noteworthy, one would need to eat these food sources every day in order to get enough vitamin D.
What Is a Normal Vitamin D Level?
Normal vitamin D requirements and blood levels vary by age because the skin’s ability to absorb and convert vitamin D to the active form diminishes with older age. Requirements also increase during pregnancy and breastfeeding.
The table below details the minimum amounts of vitamin D someone needs to get or consume per day based on international units (IU).
| Age | Amount |
| 0-12 months old | 10 micrograms or 400 IU |
| 1-70 years old | 15 micrograms or 600 IU |
| 71+ years old | 20 micrograms or 800 IU |
However, these values probably mean little because vitamin D is quantified by grams on food labels if added. Thus, rather than focus on trying to consume a certain or acquire a certain amount of vitamin D, it can be easier to get a blood test that reveals the body’s vitamin D levels.
Most scientific literature exclaims that any level of vitamin D over 20nmol/l is sufficient. However, some professionals prefer to see levels above 30nmol/l. The following table shows ranges for low, normal, and high levels for the average adult:
| Level | Amount in Blood |
| Low | 30 nmol/l |
| Adequate | 50 nmol/l |
| High | 125 nmol/l |
Symptoms of Low Vitamin D
Vitamin D is well known for helping the body absorb calcium and phosphorus for the maintenance of strong bones. However, vitamin D also contributes to the health of many other organs tissues such as muscles, nerves, the brain and the immune system.
The vitamin may also help prevent certain kinds of cancers like prostate and breast and influence diabetes, hypertension, and multiple sclerosis. Thus, most low vitamin D symptoms revolve around one of these issues.
Bone Weakening
A deficiency of vitamin D is known as Ricketts. This lack of vitamin D causes a mineralization defect of the skeleton, leading to weak, brittle bones. This is why the most common symptoms of vitamin D deficiency include bone aches and muscle weakness.
If left unattended, vitamin D deficiency can drastically affect children and adults to some extent. In children, the deficiency can cause growth retardation, widening of the long bones (like the femur, tibia, humerus, etc.), and obvious bowing and bending of the legs. In adults, vitamin D deficiency increases the risk of osteoporosis and osteopenia.
Vitamin D Supplementation
Vitamin D supplementation is not necessary for everyone. However, the majority of those living in the United States do not acquire enough, deeming supplementation smart.
Folks unable to obtain enough quality sunlight (10am – 4pm) and/or who do not eat food sources high in vitamin D should highly consider supplementation.
What’s more, because vitamin D levels are implicated in optimal immune function, it could be prudent for most everyone to get a little extra given the state of the country. The winter season offers yet another reason to consider supplementing with this potent nutrient.
Furthermore, skin color can affect the ability to absorb sufficient vitamin D. People with darker skin, aka more melanin, have a natural “sunscreen” that protects against the sun’s UV rays (3). While this serves as good sunburn and skin cancer prevention, it is not good for vitamin D absorption. Thus, any people of color should highly consider supplementation and/or will need to spend more time in the sun to reap the full benefits.
Additionally, the Department of Health recommends a few specific populations take vitamin D supplementation including:
- Breastfed babies from birth to 1 year of age
- Children aged 1-4 years old
- Everyone of any age during late autumn and winter (about October to March/April)
Finally, much research points out that supplementation of 10 micrograms/day is enough for the average person. The safe upper limit of vitamin D supplementation is 100 micrograms/day (4). It is best to work with a qualified health professional like a doctor or registered dietitian to determine proper dosage.
Good news, though… Overdosing on vitamin D from the sunlight is not possible!
The Bottom Line
Vitamin D is needed for a variety of bodily functions from proper bone maintenance to improving the immune system.
While obtaining midday sunlight for 10 to 30 minutes/day is the best and most natural way to get enough, eating foods high in vitamin D like fatty fish nearly every day can also supply sufficient amounts.
A deficiency of vitamin D, known as Ricketts, causes weak bones and sore muscles and is also implicated or related to a variety of other ailments such as hypertension and diabetes. Thus, it is imperative to monitor blood levels of vitamin D to ensure adequacy.
Finally, people tend to spend less time outdoors in the winter and related to the pandemic. This makes it probably a good idea for most people to supplement with a healthy dose of vitamin D!
References:
Fletcher J. Normal vitamin D levels: Ranges by age. Medicalnewstoday.com. Published July 10, 2020. http://www.medicalnewstoday.com/articles/normal-vitamin-d-levels.
Holick MF. Vitamin D: A millenium perspective: Vitamin D. J Cell Biochem. 2003;88(2):296-307.
Raman R, MS, RD. How to safely get vitamin D from the sun. Healthline.com. Published April 28, 2018. http://www.healthline.com/nutrition/vitamin-d-from-sun.
Vitamins and minerals – Vitamin D. Nhs.uk. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/.
