Vitamin D Deficiency During Colder Months: Impact of Living Above the 37th Parallel

The possibility of a vitamin D deficiency may be significant depending on your geographical location.

In regions where daylight hours diminish and the sky becomes more overcast during autumn and winter, it's important to consider strategies to augment one's intake of vitamin D.

Due observational studies, it is known that people residing in the northern parts of the U.S tend to be more susceptible to vitamin D deficiency owing to a dearth of sunshine.

“Elements such as geography contribute [to Vitamin D deficiency] by reducing the exposure to the sun particularly in the Northern Hemisphere during the wintertime and also because less skin is exposed during colder seasons,” says D. Allan Butterfield, PhD, an alumni association endowed professor of biological chemistry at the University of Kentucky and a contributor to various studies related to Vitamin D.

"Furthermore, irrespective of location, the use of skin products with high skin protective elements could diminish the production of vitamin D instigated by the skin,” he pointed out.

This becomes particularly worrying as a substantial proportion of the U.S population is consistently deficient in vitamin D throughout the year. A certain study discovered that almost 41% of individuals had a deficiency in vitamin D, while 22% were moderately deficient.

If left unaddressed, deficiencies like these can adversely affect bone health leading to fractures and contribute to cardiovascular health, risk of autoimmune diseases, and cognitive functioning.

The level of vitamin D in your system might even escalate your mortality risk—one particular research noted that nearly 13% of all mortalities in the U.S. could be assigned to vitamin D levels falling below 75 nmol/L.

Let's find out which states are most affected by the lack of sunshine, how much vitamin D is suggested, and ways to boost your vitamin D intake.

In certain conditions, humans are capable of producing a considerable amount of their required vitamin D from sunlight exposure on their skin. According to the World Health Organization, an exposure of five to 15 minutes to sunlight on hands, face, and arms two to three times a week during the summer months is sufficient for maintaining high levels of Vitamin D.

However, accomplishing this becomes almost impossible during the colder months, particularly if you live above the 37th parallel (37 degrees north latitude). Not only is it too cold to expose sufficient skin during the winter, but the sun’s UVB rays are inadequate as well.

If the lack of sunlight is not compensated for, by the end of winter your vitamin D reserves might be notably diminished.

“Along the 37th parallel, during the colder months...the sun is lower and its UVB rays are weaker compared to the summer,” Danielle Banks, a meteorologist with The Weather Channel stated.

Consequently, even if you spent time outside, the sunlight required to produce vitamin D may not be potent enough to enable the process.

Should your vitamin D intake prove to be insufficient, you are at risk of vitamin D deficiency.

This not only predisposes you to a slew of health problems but also complicates your body's ability to absorb and regulate calcium levels, stated Lauren Twigge, MCN, RDN, LD, a registered dietitian.

A deficit in vitamin D and calcium particularly impacts your bones. Twigge elucidated that when your bones are not supplied with the necessary calcium, your system may extract the little calcium that is present from the bones themselves.

“This process leads to frail bones which can deform and bow in children, a disease known as rickets, and soft bones in adults, called osteomalacia,” she explained.

To make matters worse, a deficiency in vitamin D can go unnoticed or it may appear as a chronic illness.

“[You may experience] discomfort and pain in your bones and muscles, nerve tingling in your hands and feet, a history of bone breaks, and even bowed and brittle bones in cases of severe deficiency,” shared Twigge.

The amount of vitamin D you require depends on various factors such as your age, skin color, and your state of health.

One study noted that non-Hispanic Black Americans, women, and people aged between 20 to 29 years old are particularly prone to a deficiency in vitamin D.

It's important to remember that how much sunlight you get during the warmer months will influence the quantity of vitamin D you will need during winter.

According to the National Institutes of Health (NIH), the recommended daily intake of vitamin D for those aged 1 to 70 is 600 international units (IU)—through food, supplements or a combination of both. Meanwhile, individuals aged above 70 require 800 IU or 20 micrograms per day.

Nonetheless, several medical experts opine that people need a higher dosage of vitamin D than that suggested by the NIH.

The Endocrine Society advocates that children and teens aged between 1 and 18, and adults up until 70 necessitate at least 600 IU daily. Conversely, adults aged over 70 require at least 800 IU daily, although they suggest that a daily intake of 1,000 IU for children and teens and 1,500–2,000 IU for adults is needed to maintain optimum blood levels of vitamin D.

To determine how much vitamin D your body needs, it’s best to talk with a healthcare provider. They can measure your vitamin D levels with a simple blood test and then make recommendations based on your personal data.

Not only will this allow them to help you best supplement vitamin D needs, but also ensure you don’t overdo it, as vitamin D can build up in the body and have negative side effects should you get too much.

While spending time in the sun is one of the best ways to boost your vitamin D levels, sun damage and a lack of sunlight in the winter months make this difficult to balance.

For this reason, during the spring and summer months, most experts recommend a maximum of 30 minutes of unprotected sun exposure each day to boost your vitamin D levels.

In the winter, you will need to rely on food and supplements to get the vitamin D you need.

Unfortunately, not many foods contain vitamin D, explained Twigge. But you will find it in fortified foods like cereals, milk, orange juice, and some plant-based milks. You also can try eating fatty fish (like salmon, tuna, and mackerel) as well as beef liver, egg yolks, some mushrooms, and fish oils.

“It is important to include nutrient-dense food sources of vitamin D because, unlike most supplements, and even the sunlight, food offers our body more than just one nutrient and these nutrients interact with one another driving digestion, absorption, and metabolism,” Twigge said.

If you opt for supplements, make sure you discuss how much you should take with a healthcare provider.

And, be sure to take it with your meals, Twigge explained. “To make the most of your vitamin D supplement, try to take it with fat-containing meals because vitamin D is better absorbed with dietary fat.”