Vitamin D

Vitamin D is a fat soluble vitamin that is essential for bone health and immunity. Like other fat soluble vitamins, and unlike water soluble vitamins such as vitamin C and the B vitamins, you do not need to absorb vitamin D every day to stay healthy and your body’s stores of fat soluble vitamins take longer to deplete than water soluble vitamins. 

Insufficient vitamin D levels is common in New Zealand. In September each year the majority of the population who were not fortunate enough to have had a sunny winter holiday, will have insufficient vitamin D levels.  However, during the summer months most New Zealanders, with some exceptions, will have sufficient vitamin D status. Vitamin D status is measured by a blood test. In healthy people it is normal for your vitamin D levels to varying throughout the year.

Vitamin D deficiency does occur. In children vitamin D deficiency presents as rickets or osteomalacia which looks like bow legs but may also present with delayed growth and bone pain.  The 2002 New Zealand National Children’s Nutrition Survey found that 4% of children were deficient and that 31% had insufficient vitamin D levels. The 2006 adult National Nutrition Survey found that similar numbers of adults were deficient and that up to 45 – 52% of adults had insufficient vitamin D levels. Vitamin D status varies by location, New Zealanders in the north typically have higher levels than New Zealanders in the south, and by ethnicity or cultural practices, if you have darker skin or cover your skin your vitamin D levels tend to be lower. Vitamin D deficiency is also more common in people with chronic inflammation such as IBD and in people who need to avoid the sun because their medication increases their risk of skin burn such as IBD immunosuppressant medications azathioprine, thioguanine and methotrexate. 

Your body can make vitamin D from sunlight! But not all year

Vitamin D is the only vitamin that the body can make from sunlight! UVB radiation from the sun directly on your skin results in a chemical reaction that converts 7-dehydrocholesterol through a couple of steps to the active form 1,25 dihydroxyvitamin D (calcitriol). Interestingly, this process occurs in all animals with a vertebrae.

As you may have guessed, your body can only make vitamin D if your skin is touched by sunlight and if the Earth is close enough to the sun for the UVB rays reach your skin. This is why people in the South Island of New Zealand have lower levels than those in the North Island because for six months of the year on cloudy days the UV index is less than 3 (green shaded areas on the diagram). When the UV index is three or less there is not enough UVB rays on your skin to make vitamin D. Furthermore, during summer the UV rays are so harsh in New Zealand that we need to cover our skin with sunscreen or clothing to reduce our risk of sun burn and skin cancer.  For more information about the UV index on any particular day see the NIWA website.  

The Ministry of Health recommends that you expose your skin (face and hands/arms/legs) to sunlight before 10am between September and April. People with lighter skin need less sunlight exposure than people with darker skin. Younger people need less sunlight exposure than older people. The general recommendation is that 10-30 minutes of sunlight in summer is enough to make sufficient vitamin D. It must be outside sunlight, you cannot make vitamin D with sunlight that passes through a window glass. 

Your body can make vitamin D from sunlight for approximately six months of the year but how can you get enough vitamin D for the remaining months to prevent your vitamin D levels from becoming low?

There is vitamin D in some foods

Animals, the same as humans, produce Vitamin D from sunlight. This vitamin D is stored in the liver until the body needs it. Therefore, animal liver is a great source of Vitamin D but so is eggs, oily fish (such as salmon, sardines, eel, warehou), and some milk and milk products. The amount of vitamin D in these foods depends on what the animals or fish eat/are fed and how much time they spend in the sun. Hens who spend time outside each day will lay eggs that are higher in vitamin D than battery hen eggs. Also, if hens are fed vitamin D fortified food (food that has a vitamin D supplement added to it) their eggs will contain more vitamin D. Eggs are a great source of vitamin D during the winter months - eating two eggs could provide you with 50 - 100% of your daily vitamin D needs! Eating eggs at least a few times a week is a great way to improve your vitamin D intake.

The food industry also voluntarily fortifies (adds a vitamin or mineral supplement) margarine and some other dairy products and soy drinks with vitamin D and vitamin A. Fortifying foods with added vitamins and minerals is a common way for governments to improve the publics’ health. For example, in the 1990s goitre (enlargement of the thyroid gland causing a large lump in the neck) due to iodine deficiency becoming more common. In response to this the government made it compulsory for all bread to be made with iodised salt (salt that is fortified with iodine).  Now iodine deficiency and goitre are less common and the iodine status of New Zealanders is much improved. Margarine and butter (although I could not find any butter with vitamin D added at my supermarket) was first fortified with vitamin D to prevent rickets in children. Not all companies fortify their products so check the nutrition information panel and ingredient list for vitamin D to ensure you buy a fortified product. Two teaspoons of fortified margarine or butter provides you with 10% (1mg) of your daily vitamin D needs. 

There is one plant food that makes vitamin D when exposed to UVB light; mushrooms! Mushrooms that are either commercially exposed to UVB lights or that you put outside in the sun produce lots of vitamin D. The mushrooms may change colour slightly but this does not affect the flavour or quality of the mushroom. Unfortunately New Zealand commercial mushroom producers do not expose their mushrooms to UV lights but during the summer months you can do this at your own house. After buying your mushrooms, leave them outside in the sunlight for an hour and a chemical reaction will occur to make vitamin D. Remember though, that UVB rays do not go through glass so mushrooms on the windowsill will not make vitamin D.

Vitamin D and inflammatory bowel disease

There is a lot of research that suggests that vitamin D deficiency is more common in people with IBD. Many of the research studies though are not well designed which makes it difficult for us to say whether New Zealanders with IBD are more likely to be vitamin D deficient than the general New Zealand population. 

There is also plenty of research that suggests that insufficient levels of vitamin D (<50 nmol/L) is associated with active IBD. Again, many of these studies are poorly designed so we are not sure if it is the chicken or the egg, that is, does insufficient vitamin D status promote active disease or is it caused by active disease. 

We do know, however, that taking an oral vitamin D supplement improves vitamin D status and gets blood vitamin D levels up into the optimal range of 50-100 nmol/L. We also know that large one-off doses of vitamin D are safe (see my research page for our publication on this topic in children with IBD or click here). The benefit of this treatment is that you don’t have to remember to take another tablet once a week or once a month. 

There are currently high quality clinical trials that are investigating whether taking a vitamin D supplement reduces inflammation in ulcerative colitis. In the coming years we will know more about the possible role of vitamin D in immune function and IBD. In the meantime, get your vitamin D levels checked and make some of the dietary changes described below to optimise your vitamin D intake from food.

When should you take a vitamin D supplement?

If you are vitamin D deficient you need to a take a vitamin D supplement. This is available on prescription from your GP, specialist or dietitian. Some New Zealanders do need a regular take a vitamin D supplement. You can find out more on the Ministry of Health website here.

People with IBD who are on immunosuppressant medication and avoid sunlight or people taking long courses of corticosteroids (to protect your bones from the side effects of the medication) may need an ongoing vitamin D supplement – discuss this with your GP, specialist or dietitian.

Take home messages

- eat eggs more often (see recipe idea below) to increase your vitamin D intake from food

- buy dairy and plant-based dairy alternatives (margarine, plant milks, tofu) that are fortified with vitamin D

- try sunbathing your mushrooms outside!

- maximise your vitamin D levels from October to March by getting sunlight on your skin before 10am and then use usual sun protection strategies to protect your skin from sun burn and damage

- if you have Crohn’s or colitis you should have your vitamin D status checked with a blood test annually. Your levels will be lowest in September/October because your stores of vitamin D will have depleted over winter. 

Shakshuka

This version of baked eggs is a traditional North African dish. There are many cultural variations on baked eggs and they are all delicious! 

3 Tbsp olive oil
1 tsp cumin seeds
1 garlic clove finely diced
2 red capsicums finely sliced (I used a jar of charred grilled capsicums)
400g can of chopped tomatoes
½ tsp sugar/honey (if using a jar of capsicum)
½ tsp hot smoked paprika
A pinch of saffron strands
Juice of ½ lemon
4 eggs
Salt and pepper to taste

1. Heat oil and roast cumin seeds until fragrant

2. Add garlic and peppers and cook on a low heat for 10 (if using prepared) – 20 minutes (if using fresh)

3. Add tomatoes, sugar/honey (if using), paprika and cook over a low heat for 15 minutes.

4. Season with lemon juice, salt and pepper

5. Make a well and crack egg into each well

6. Bake at 180°C for 10 minutes or until egg is just set

7. Serve on toast with a green salad or parsley