Vitamin D: The Sunshine Vitamin

Melaine Hendershott | Oncology Dietitian, MS, RDN, CSO

May 24, 2023

As the winter season comes to an end, we experience a dramatic transition from dark and cold to warm and bright. This shift inspires many of us to get outside more and enjoy the sun. The sun not only provides light and warmth – it is also the primary source of an important nutrient: vitamin D, or calciferol. Vitamin D is a fat-soluble vitamin when consumed orally in foods such as fatty fish, eggs, mushrooms, and fortified milk or orange juice, or in supplements. It is also produced by our own bodies as a result of sun exposure on our skin.

Functions of Vitamin D

The primary function of vitamin D is to promote calcium absorption in the gut, which is directly related to bone health. Without sufficient vitamin D, our bones can become brittle or misshapen. Vitamin D is important for the prevention of osteoporosis, and it also has other roles such as reducing inflammation and immune function. There is more and more emerging research on its role in disease prevention.

Forms of Vitamin D

There are two primary forms of vitamin D: D2 (ergocalciferol) and D3 (cholecalciferol). Both forms are absorbed well, and both are found in supplemental form. These two forms of vitamin D are found to be equal in their ability to raise blood levels of vitamin D.

Vitamin D Blood Levels

In the state of Colorado and other states with more northern latitudes, not much vitamin D is produced by the skin in the months between November to March, when the sun is lower on the horizon, and when we often do not have much skin exposed during these months. Early spring is a great time to have your blood levels of vitamin D checked, as they should be about the lowest of the year. See Table 1 at this link for vitamin D concentration levels and their associated health status.

How Much Vitamin D Is Needed?

Vitamin D supplements usually provide between 400 IU per day – 5,000 IU per day. There is differing opinion on how much vitamin D to take in supplement form. The Endocrine Society, for example, recommends 1500 – 2000 IU per day to maintain a healthy blood level, and the United Kingdom recommends 400 IU/day for those over 4 years of age. It’s important to note that just 15 minutes a day of sun exposure in summer months can provide sufficient vitamin D in most cases. See Table 2 at this link for recommended daily allowances (RDA) of vitamin D.

Vitamin D and Cancer

Vitamin D seems to play an important role in cancer prevention and survivorship. In recent studies, vitamin D was found to be perhaps less important in primary prevention (no difference between placebo group and vitamin D group over 5 years), but it did decrease cancer mortality by 13%. In breast cancer survivors, a higher blood level of vitamin D has been shown to decrease risk of all-cause mortality by 7% and breast cancer mortality by 3%. There also seems to be rising evidence that adequate blood levels of vitamin D help to prevent colorectal cancers.

Can You Get Too Much Vitamin D?

Yes, excessive amounts of vitamin D in your blood can lead to hypercalcemia. Symptoms include nausea, vomiting, muscle weakness, pain, loss of appetite, dehydration, excessive thirst and kidney stones. However, this condition is rare and usually found in those supplementing at greater than 10,000 IU per day.

Vitamin D: Final Tips

If you are wondering if you have enough vitamin D, get a blood test. If it is low, talk to your doctor or dietitian about appropriate supplementation. You can get your vitamin D checked every 2-3 months until your blood levels come up to normal.