Vitamin D levels & Winter

Vitamin D is unique amongst vitamins.   It is the only one that requires sufficient sunlight in order to be synthesized or made within our body. 

The sun’s ultraviolet B (UVB) rays or “tanning rays” are what trigger the skin to produce vitamin D.  These rays are stronger near the equator and weaker at higher latitudes.  That is why the fall and winter months can be a challenge for anyone who lives north of the 37th degree latitude to obtain an adequate amount of the sunshine vitamin.   For anyone living north of the line connecting San Francisco to Philadelphia they will not be able to produce vitamin D from the sun during the months of November through March.  Anyone living in the southern regions of the U.S. such as Los Angeles or Orlando will be able to synthesize vitamin D year round.

Why does it matter to get enough vitamin D?

The short answer is sufficient levels of vitamin D are necessary to absorb calcium helping to prevent the brittle bone disease of osteoporosis.  But it has also been shown to possibly play a role in preventing heart disease, cancer, Alzheimer’s disease, strokes, high blood pressure, diabetes, multiple sclerosis, and may slow the aging process.

Worldwide, it is estimated 1 billion people have inadequate levels of vitamin D in their blood and deficiencies can be found in all ethnicities and age groups. 

Sources of vitamin D

There really is a good reason why vitamin D is nicknamed the ‘sunshine’ vitamin.  The best way to get vitamin D is naturally from the sun.  Large amounts of vitamin D3 (cholecalciferol) are made in the skin when it is exposed to the sun. 

There are only a few natural food sources of vitamin D - the flesh of fatty fish such as salmon, tuna, and mackerel or fish liver oils are the best food sources.  Other natural food sources include beef liver, egg yolks and cheese.  Otherwise, foods such as milk and yogurt have been fortified with vitamin D but do not contain it naturally.

How long do we have to be exposed to sunlight?

Exposure time depends on the skin tone of each individual.  People with very fair skin may only need about 10 minutes of time in the sun for their body to produce vitamin D.  Those who have very dark skin may require up to at least 30 minutes of being in the sun or longer in order to make vitamin D.  For the average person, 15-20 minutes at least 3 times a week where at least their face, arms and or legs are exposed is sufficient for their body to obtain enough vitamin D.   However, the more skin that is exposed, the more vitamin D you will make.  A person does not need to tan or burn to get the vitamin D they need. 

Another factor affecting the amount of vitamin D skin will make is the time of day.  The best time of day to be out in the sun in order for skin to produce the most vitamin D is midday or 12 noon when your shadow is the shortest.

What can a person do during the fall/winter months to get sufficient vitamin D?

Here are the best suggestions on getting through the long winter months without becoming “D-ficient:”

·        If you live below the 37th degree latitude, you should be able to make vitamin D most of the year.  Try to get outdoor several times a week if not daily for a 15 minute walk in the sun at midday.

·        Include good food sources of vitamin D daily – salmon, tuna, mackerel, mushrooms, eggs, cheese, and vitamin D fortified foods such as milk (cow, almond, soy, or coconut milk are all fortified), yogurt, and some orange juices.   A 4-ounce serving of salmon provides 265% of the daily amount recommended of vitamin D. 

·        Take a supplement of vitamin D3.  Check with your physician on their recommendation of what amount to take.