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Keep your immune system strong with vitamin D

Updated: Sep 20, 2021

Did you know that vitamin D is a hormone? When the rays of the sun hit your skin, vitamin D is produced as a response to the sunlight. We also get vitamin D from the food we eat, but only about 10% is taken up in our bodies this way.

We’ve all heard that a vitamin D deficiency causes rickets in children and osteomalacia – softening of the bones – in adults. Too low levels of the vitamin means we’re unable to maintain enough calcium in our blood for healthy bone growth. (1)

But emerging research suggests that a lack of vitamin D is also linked to a weaker immune system, fatigue, bone and back pain, and depression. (2)

In fact, one the most important functions of vitamin D is to help us fight viruses and bacteria. According to this research paper, it works directly with the cells that are responsible for combating infection. (3)

A number of observational studies point to a connection between a vitamin D deficiency and respiratory tract infections, such as colds and pneumonia. (4, 5)

It also looks like the good old D can help fight off Covid-19. Auckland-based pharmacist and metabolic researcher Dr Catherine Crofts has published research about the importance of keeping your vitamin D levels up – and keeping insulin levels down – to help with Covid-19.

“It’s not just going to help should we get Covid-19, it will actually help to boost the effectiveness of the vaccine,” says Dr Crofts. “Having adequate amounts of vitamin D also helps to mitigate the effects of flu and other respiratory viruses over winter.” (6)

How to get enough vitamin D and boost your immune system:

· Spend some time in the sun – but don’t get burnt!

I’m not arguing with the idea of protecting ourselves from UV radiation, but we have perhaps become too diligent with the sunscreen and covering up. Nearly a third (27%) of New Zealanders are below the recommended blood level of vitamin D, according to the Ministry of Health. (7) You can’t manufacture vitamin D if you’re wearing sunscreen, says Dr Crofts. Try to get outside during the day (especially in winter) and soak up some of that sun!

· Eat some fish and seafood, like salmon, tuna, mackerel, oysters, shrimp, sardines and anchovies

· Eat some mushrooms!

Interestingly, just like humans, mushrooms also produce vitamin D when exposed to UV light.

· Egg yolks are rich in vitamin D

Stay healthy!

Ulrika Hedquist Ballinger is a writer and an instructor at Vitality Lab.

She is currently training to become a Health Coach.


1. You and your hormones – Vitamin D,

2. 8 Signs and Symptoms of Vitamin D Deficiency, Healthline,

3 Martens et al, Vitamin D’s Effect on Immune Function,

4 Kana Ram Jat, Vitamin D deficiency and lower respiratory tract infections in children: a systematic review and meta-analysis of observational studies,

5 Pletz et al, Vitamin D deficiency in community-acquired pneumonia: low levels of 1,25(OH)2 D are associated with disease severity,

6 Dr Catherine Crofts, Vitamin D helps fight Covid-19, says research,

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