Vitamin D has long been recognized as a major bone-building nutrient, required for calcium absorption and bone health.

But recent revelations about D’s role as a hormone have led scientists to view this nutrient in a whole new light.

A large and expanding body of research has suggested links between vitamin D status and immune diseases like multiple sclerosis and arthritis, as well as between D and chronic diseases such as cardiovascular disease and type 2 diabetes.

More recently, vitamin D has been considered for its role in cancer prevention and survival.

Vitamin D is known as the “sunshine vitamin,” because we can make it ourselves through a chemical reaction that happens in the skin when exposed to ultraviolet B (UVB) light. Individuals living in very sunny climates relatively close to the equator may be able to synthesize enough vitamin D to meet their needs throughout the year — if they get regular sun exposure.

However, vitamin D synthesis from the sun is not possible during most of the winter months for people living at a latitude of more than 40 degrees N or 40 degrees S. This mean all Oregonians need to consume enough food sources or supplemental vitamin D daily between November and March to maintain healthy blood levels of the vitamin.

Other factors influencing vitamin D synthesis include time of day and level of sun exposure. More of the vitamin is made when the sun’s rays are strongest, generally from 10 a.m. to 3 p.m. during the summer. On overcast days, production may be non-existent.

Individuals with darker skin have a more difficult time making vitamin D because higher levels of melanin in darker skin blocks UV penetration. As you might expect, wearing protective clothing and sunscreen (with SPF greater than 8) limits vitamin D production. Beyond age 50, the need for vitamin D increases. It is estimated that adults experience a four-fold decrease in capacity to synthesize vitamin D from the sun by age 65.

Older people may be less likely to get outside, and often have reduced food intake, putting them at greater risk for low blood levels of vitamin D. Having higher levels of body fat does not affect the skin’s capacity to synthesize vitamin D, but greater amounts stored under the skin cause more of this fat soluble vitamin to be held in the fat tissue, thus interfering with its release into the circulation.

As a result of all these connections and concerns, many experts believe that current recommendations for vitamin D intake are too low. That makes sense considering reduced intake of vitamin D-containing foods, increased number of overweight people, modern lifestyles lived mostly indoors and public health initiatives that encourage the use of sunscreen to prevent skin cancer.

How Much D is Enough?

The Linus Pauling Institute at Oregon State University recommends that generally healthy adults take a multivitamin supplement that supplies at least 400 IU of vitamin D3 daily. In addition, at least 10 to 15 minutes of sun exposure on the arms and legs or face and arms at least three times a week, between 11 a.m. and 2 p.m. during the spring, summer, and fall is recommended as a way for residents of temperate latitudes (much of the U.S.) to avoid vitamin D deficiency at the end of winter.

Some experts, including endocrinologist Dr. Wei Hao of The Corvallis Clinic, believe that all adults should be taking at least 800 IU of supplemental vitamin D3 on a daily basis. The American Academy of Pediatrics has recommended that children, from newborns to teens, should get 400 IU daily, double the amount previously suggested. That includes breast-fed infants and the many teens who drink little or no milk.

If blood levels of vitamin D are found be low, Hao suggests that individuals follow their physician’s recommendations for returning levels to normal.

This may include using high weekly or monthly doses with additional blood tests to determine effectiveness of the dosing. If you are concerned about your vitamin D status, you will need to ask a medical provider who is licensed to order the blood test. The results are returned to that provider by the laboratory. The charge for testing vitamin D is $65 to $70, with many health plans covering the cost of the analysis.

The Corvallis Clinic lab manager Richard Eastburn estimates receiving over 100 orders for vitamin D testing each week, with as many as half of the patients testing in the low normal to below normal range.

Carol Walsh is a registered dietitian and certified diabetes educator who provides nutrition counseling services at The Corvallis Clinic and Albany Family & Specialty Medicine.