Vitamin D

What is it?
Vitamin D is a fat-soluble vitamin made in the skin when it is exposed to sunlight. There are two types of Vitamin D. D3, or cholecalciferol, is produced by mammals and fish, and D2, or ergocalciferol, exists in plants. Vitamin D isn’t a nutrient in the usual sense as it is supplied mainly by the skin, and if you get outside in the sun enough with your skin exposed, you don’t need to worry about dietary vitamin D.

What does it do?
The primary role of Vitamin D is to support adequate blood calcium levels by improving the small intestine’s capacity to absorb calcium from the diet. It is involved in bone health, mood, and immunity, helping to maintain healthy skin and muscle strength.

How much?
Adults 19-50 years old should get 5.0 micrograms (µg) daily, or 200 International Units (IU). Adults 51-70 need double, and those over 70 need 15 µg or 600 IU daily.

Supplements are in D2 or D3 form. There is some evidence that D3 may increase blood levels better than D2. Most people will get adequate amounts through skin exposure to the sun and won’t need to supplement.

Vitamin D is best absorbed when taken with a meal with a small amount of fat; a high-fat meal decreases absorption.

Evidence
There is no evidence supplementing with vitamin D has any benefit for arthritis.

It may aid pain and lack of function in people with fibromyalgia, but the evidence is inconclusive.

Other benefits seen with vitamin D supplementation, such as reducing falls in older people, are only seen when the individual has low vitamin D levels, to begin with.

Safety
The Upper Limit in Aotearoa New Zealand and Australia for everyone one year and older are 80µg/day, or 3200 IU. Extremely high doses of vitamin D from supplements (~20,000 IU daily) can cause vitamin D toxicity causing high levels of calcium in the blood. This can manifest in several health issues, such as weakening your bones, creating kidney stones, and interfering with brain and heart function.

Who might need to supplement?
Vitamin D deficiency is more likely to occur in winter when people aren’t going outside as much and are wearing more clothes. People under 50 can make and store enough vitamin D for six months after regular sun exposure, as is usually the case in summer which can carry them through winter. People over 50 have a reduced ability to make and store vitamin D, so they may need to supplement over the winter months.

People who, for religious or other reasons, cover up most of their skin whenever they are outside won’t be able to produce enough vitamin D and will likely need to take a supplement.

People with dark skin need more time in the sun than those with fair skin to make adequate amounts. It is estimated that for older women with fair skin, exposure of 6% of the body (face, hands, and forearm) to sunlight for 15-30 minutes without sunscreen 2-3 times per week would make the equivalent of 15 µg a day.

Talk to your doctor if you think you are not getting enough vitamin D and want to supplement.

Where can I get vitamin D?
It is made primarily in the skin with sun exposure and most efficiently without sunscreen.

From food:
cod liver oil, oily fish, eggs, fortified animal and plant milk. Fun fact: mushrooms have a small amount of vitamin D but can increase the amount through sun exposure!

Supplements: You can get a prescription through your GP and purchase from pharmacies, supermarkets, online and at health stores.