chapter 12: the power of light

Sunlight is essential for many important bodily functions, including maintaining your circadian rhythm, mood and for producing vitamin D. In Chapter 7, we learned how vital vitamin D is for strong and balanced immunity, since it is involved in a vast array of immune-system activities. Vitamin D has also been reported to regulate gene expression and further exert its immunomodulatory effects on immune cells¹⁰⁸. Also, in the skin, there are cells known as keratinocytes, which make a potent immune-nourishing substance known as interleukin-1 (IL-1), which promote the number of T cells by helping them to multiply rapidly. Natural sunlight stimulates IL-1, which is another reason why it is important we get enough sunshine.

While sunlight allows us to make vitamin D, a surprise research finding reported another significant benefit of getting some sunshine. Scientists at Georgetown University in the US, observed that sunlight, through a different mechanism to the manufacturing of vitamin D, ‘energizes’ T cells, which we know play a crucial role in our immunity¹⁰⁹. T cells need to move quickly to carry out their function and get to the infection site. The researchers discovered that low levels of blue light in the sun’s rays allows T cells to move quicker, confirming that sunlight directly activates our important immune cells, by enhancing their movement.

Studies have shown that autoimmune diseases tend to share a predisposition for vitamin D deficiency, which negatively alters the gut microbiome and the integrity of the gut barrier¹¹⁰. Low vitamin D appears to increase the permeability of the gut barrier and heighten immune activity – remember our goal is balanced immune activity. This, in turn, alters microbial composition and the ability of our microbes to move across the gut barrier, leading to negative interaction with the immune system. However, fortunately, researchers have reported that the composition of the gut microbiome can be positively impacted by vitamin D status and exposure¹¹¹. Further, scientists have confirmed that it is clear that the immune system and microbiome are very closely connected, and that vitamin D is a key mediator in this dynamic¹¹⁰.

Vitamin D deficiency

Vitamin D deficiency is a global health problem caused mainly by insufficient exposure to sunlight, and it is estimated that about 1 billion people globally have low levels of the vitamin in their blood¹¹². According to a 2011 study, 41.6 per cent of adults in the US are deficient¹¹³. However, many people are unaware that they may even have such a deficiency. For most people, exposing your arms and face for 10–15 minutes a few times a week and eating oily, fatty fish twice a week, is sufficient to maintain your vitamin D levels.

To supplement or not

Taking a vitamin D supplement in winter may be recommended for some individuals, especially if a blood check highlights you are deficient. If you do decide to supplement, just be cautious, as it is possible to take too much vitamin D, particularly if you take a high-dose supplement, and/or for a prolonged duration. This can result in a build-up of calcium in the body, which can damage your bones, heart and kidneys. If you suspect a vitamin D deficiency, I would suggest speaking with your medical practitioner who may advise you to have a blood test to check your levels. Once you know for sure you need to supplement, you can go from there, as too much can be as detrimental as too little – we are aiming for balance.