Vitamin D: The Sunshine Hormone and RA

Today is a glorious, sunny day. Sure, it’s still cold. Brrrrrrrr. But more than one living creature in our household is finding treasured sunny spots in which to lie and soak up the rays.

What is vitamin D?

I was standing in the bathroom, letting the sun warm my back, when my thoughts wandered to summertime, sunshine, and eventually vitamin D.

Vitamin D is fat-soluble vitamin found in a small number of foods. It is also a hormone synthesized in the body when sunlight, specifically ultraviolet B (UV-B) light, reaches exposed skin. Many people do not get enough vitamin D through sun exposure and food alone so they take dietary supplements¹.

I am one of those persons.

The relationship to RA

Being diagnosed with multiple autoimmune diseases, some of which have been associated with vitamin D deficiency, makes getting enough vitamin D important. With rheumatoid arthritis, reduced vitamin D intake has been linked to increased risk of developing the disease, and vitamin D deficiency has been found to be associated with disease activity and musculoskeletal pain in patients with RA².

Although it was my primary care doctor who first checked my vitamin D levels, it is my rheumatologist and neurologist who monitor my D levels and suggest how much I should take daily.

Since I take methotrexate, a drug which contributes to drug-induced photosensitivity reactions, I need to get my vitamin D in other ways besides the sun. Patients who use methotrexate are instructed to protect their skin from direct sun exposure to avoid phototoxic skin reactions. The SPF protection provided by many sunscreens blocks UV-B light, the type which causes a typical sunburn; but drug-induced photosensitivity reactions are more often caused by UV-A light.

How does it work?

Vitamin D circulates in the body in two forms. The liver converts vitamin D to 25-hydroxyvitamin D3 [25(OH)D3], also known as calcidiol. The kidneys convert calcidiol to activated vitamin D, also known as 1,25-dihydroxyvitamin D [1,25(OH)₂D] or calcitriol.

The recommended test that measures vitamin D levels in the blood measures the serum concentration of 25(OH)D3 that is reported as nanomoles per liter (nmol/L) or nanograms per milliter (ng/mL). The following cut-off points are based on a review of data conducted by a committee of the Institute of Medicine (IOM), not by a scientific consensus process¹.

• <30 nmol/L or <12 ng/mL is associated with vitamin D deficiency
• >50 nmol/L or >20 ng/mL is generally considered adequate for bone and overall health in healthy individuals
• Emerging evidence indicates that >125 nmol/L or >50 ng/mL is associated with potential adverse effects, particularly with levels >150 nmol/L or >60 ng/mL

Serum levels greater than 20 ng/mL are considered adequate for about 97.5% of the population, according to the IOM report, and levels greater than 50 ng/mL may cause undesirable adverse effects. However, some rheumatologists (including my own) recommend serum concentrations between 50-80 ng/mL in patients diagnosed with autoimmune disease.

My 25(OH)D3 serum level was 70.3 ng/mL the last time it was tested after years of monitored vitamin D supplementation, whereas it was 7.6 ng/mL at the time I was diagnosed with RA and experiencing a great deal of pain.

How much is enough?

I am looking forward to being able to enjoy the sunshine a bit more as the weather warms up. However, I will continue to protect my skin from ultraviolet light and take vitamin D3 supplements each day.

To know how much vitamin D3 you may need to take, please talk to your doctor. It is important to have your blood tested to know where you are starting from before starting on a regimen to increase your levels. For those who are interested, I take a daily supplement of 10,000 IU vitamin D3. My body’s need for vitamin D supplementation is increased by being obese.