If you have psoriatic arthritis (PsA), you may wonder if there is a certain diet or certain supplements that will improve your condition. In particular, you may wonder about vitamin D, the so-called “sunshine” vitamin. The truth is, studies are mixed as to whether or not vitamin D can help your psoriatic arthritis, especially if you don’t already have low levels. Here’s what the research shows.
Why Is Vitamin D Important for Psoriatic Arthritis?
Vitamin D is important for your overall health. It helps your body retain calcium and phosphorus, both of which are important to build bone. But it also may help reduce inflammation, which is thought to play a role in the development of psoriatic arthritis.
Research suggests that vitamin D can help reduce inflammation that can lead to PsA in several ways:
- It suppresses the production of three inflammatory chemicals made by your body: IL-2, IL-6, and interferon gamma.
- It promotes suppressor T-cell activity. This is a type of immune cell that prevents your immune system from going into overdrive.
- It ramps down the production of natural killer cells, which have been associated with PsA.
Vitamin D supplements have been used for more than 60 years to treat psoriasis, another condition often associated with psoriatic arthritis. But doctors don't typically recommend high doses of vitamin D to treat this skin disease. Very high levels of vitamin D in the body have been linked to high blood pressure, high blood calcium levels, and low bone density. Doctors prescribe a topical drug, calcipotriol, which is related to vitamin D and slows down the rapid skin cell production that’s associated with psoriasis. It’s very safe and effective.
What Does Research Say About Vitamin D and Psoriatic Arthritis?
The research has been mixed about vitamin D and psoriatic arthritis.
- A 2015 study published in Arthritis Research and Therapy found that almost 41% of people with PsA had a vitamin D deficiency compared to 26.7% of a control group.
- A 2021 Portuguese study published in Annals of Rheumatic Disease looked at patients with PsA who had just started a biologic and found that those whose vitamin D levels were at or higher than 30 ng/mL had a better response to treatment.
- A 2018 study published in JAMA Dermatology by the Medical Board of the National Psoriasis Foundation looked at 55 studies of over 4,500 patients from 2014 to 2017. The Board concluded that there wasn’t good evidence to support the use of vitamin D supplements for psoriasis. There wasn’t any benefit to taking vitamin D to improve psoriasis over a period of under 6 months, although some studies did show it could help for longer than that in patients with plaque or erythrodermic psoriasis. There were very few studies on vitamin D supplementation and psoriatic arthritis, and those didn’t show a benefit.
The National Psoriasis Foundation says that research on whether or not vitamin D can help alleviate psoriatic symptoms is small and limited.A 2020 review published in the journal Nutrients concluded that there just isn’t good research on vitamin D supplementation and PsA.
Should You Take Vitamin D to Treat Your Psoriatic Arthritis?
The medical board of the National Psoriasis Foundation doesn’t recommend vitamin D supplements to prevent or treat psoriatic disease in people who have normal vitamin D levels.
It’s a good idea, however, to talk to your doctor and have your blood levels of vitamin D checked. Almost 1 out of 4 people in the United States have vitamin D blood levels that are too low for their overall health. If your levels are at least 20 ng/mL, they are adequate. It’s not recommended that you go above 50 ng/mL. That can cause health problems such as:
- Nausea and vomiting
- Muscle weakness
- Loss of appetite
- Kidney stones
Extremely high levels can cause kidney failure, irregular heartbeat, and even death.
You can’t get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes. It’s also very hard to get too much vitamin D from food. The main way this happens is if you take too high of a supplement.
What’s the Best Way to Get Vitamin D?
The National Psoriasis Foundation says that the safest source of vitamin D is food. Good sources include:
- 3 ounces of salmon (anywhere from 383-570 IU)
- 3 ounces of canned light tuna (231 IU)
- A cup of fortified soy milk (120 IU)
- A cup of fortified skim milk (115 IU)
- A cup of fortified orange juice (100 IU)
- A cup of low-fat yogurt (116 IU)
- 1½ ounces of American cheese (85 IU)
- A cup of raw mushrooms (anywhere from 114-1,110 IU)
You can also get vitamin D from 10 minutes of midday, unprotected sun exposure. This isn’t recommended though, as it’s been linked to skin cancer.
How Much Vitamin D Do I Need if I Have Psoriatic Arthritis?
If you’re not deficient, the National Institutes of Health recommends all adults age 70 and under get 600 IU a day. If you’re older than that, you’ll need to get 800 IU a day.
If you are deficient – meaning your blood levels are under 20 ng/mL – then you should talk to your doctor about taking a vitamin D supplement. It’s found in multivitamin supplements but is also available as a standalone supplement. The two forms of vitamin D available are D2 (ergocalciferol) and D3 (cholecalciferol). Both types will increase your blood vitamin D levels, but D3 is generally recommended as it raises it higher and for longer than D2.
Since vitamin D is fat-soluble, your doctor will usually recommend that you take it with a meal or snack that also contains some healthy fat, like nuts or avocado.
The following drugs have also been shown to interact with vitamin D:
- The weight loss drug orlistat can reduce vitamin D absorption from food and supplements.
- Cholesterol-lowering statins like atorvastatin, lovastatin, and simvastatin may not work as well if you take very high doses of vitamin D.
- Steroids like prednisone can lower your body’s vitamin D blood levels.
- Thiazide diuretics can raise your blood calcium level too high if you also take vitamin D.
While it’s important to take a vitamin D supplement if you are deficient to help your psoriatic arthritis, the best way to relieve PsA symptoms is to follow a healthy, low-calorie diet, especially if you are overweight.