Vitamin D & Immunity

The sunshine vitamin

Vitamin D is produced mainly by the skin through exposure to sunlight. To a lesser extent (around 20%), vitamin D comes from foods such as fortified dairy products and cereals, oily fish such as tuna and salmon, fish liver oils, red meat and eggs. Most people do not consume enough vitamin D through food, therefore levels fall during winter when sunlight exposure lessens. Vitamin D however is stored in the body, therefore levels built up in summer can somewhat be relied on during winter.

Vitamin D is a fat soluble vitamin that plays a number of roles in the body, including supporting bone and skin health, mood, and immunity. There is extensive evidence supporting vitamin D’s anti-inflammatory and immune regulating properties that help to activate the immune system defenses. Studies have shown that vitamin D enhances the function of our immune cells, including T-cells and macrophages that protect our body against pathogens. Vitamin D deficiency has been associated with increased risk of viral and bacterial respiratory infections, and supplementing with vitamin D has shown to decrease the risk of acute respiratory infections.

Vitamin D is essential for good health yet many people have low levels, which can be exacerbated during a lockdown in winter months. Support your vitamin D status by regularly consuming foods containing vitamin D and having some safe sun exposure each day. During summer, as little as 6-8 minutes before 10am and after 4pm should allow enough sunlight to be absorbed to meet your vitamin D needs. In winter, around 30 minutes in the middle of the day is required.

Guidelines for daily vitamin D intake through food are 5µg for people under 50 years old, 10µg for ages 51-70 years, and 15µg for those over 70 years. Below are some examples of how to achieve this intake:

1 tablespoon of cod liver oil = 34µg

100g salmon = 15µg

100g cooked mackerel = 11µg

100g canned tuna = 5µg

250ml fortified milk = 3µg

100g cooked beef or liver = 1.5µg

1 tablespoon fortified margarine = 1.5µg

1 cup fortified cereal = 1µg

1 egg yolk = 1µg

There is no evidence to support blanket vitamin D supplementation of New Zealander’s and consuming unnecessary high doses through supplements may have adverse effects. Supplementation should be guided by a health professional and is generally only recommended for people who cannot increase their sun exposure or intake of vitamin D containing foods, and are at high risk of deficiency (older age, housebound, people with darker skin or who are veiled). Low doses in multivitamins are considered safe. Testing vitamin D levels is generally considered unnecessary as testing is expensive and there is no consensus on the optimal vitamin D serum level.

Vitamin D isn’t the magic bullet to immunity, however is an important addition to an overall healthy diet and lifestyle. The most effective way to boost vitamin D levels is regular short (non-burning) periods of sunlight exposure to 20% of the body (eg. arms and legs).

References

Hejazi, M. E., Modarresi-Ghazani, F., & Entezari-Maleki, T. (2016). A review of Vitamin D effects on common respiratory diseases: Asthma, chronic obstructive pulmonary disease, and tuberculosis. Journal of research in pharmacy practice, 5(1), 7–15.

Hughes, D. A., & Norton, R. (2009). Vitamin D and respiratory health. Clinical and experimental immunology, 158(1), 20–25.

Prietl, B., Treiber, G., Pieber, T. R., & Amrein, K. (2013). Vitamin D and immune function. Nutrients, 5(7), 2502–2521.

Ginde AA, Mansbach JM, Camargo CA. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the third National health and nutrition examination survey. Arch Intern Med 2009;169:384–90.

Vitamin D and calcium supplementation in primary care: an update. Best Practice Journal – Issue 76.

Lanham-New S, Webb AR, Cashman KD, Buttriss JL, Fallowfield JL, Masud T, et al. Vitamin D and SARS-CoV-2 virus/COVID-19 disease. BMJ Nutrition, Prevention & Health. 2020;0.

Vitamin D supplementation: Navigating the debate. Best Practice Journal – Issue 36.