I’ve mentioned before how important vitamin D is for our immune systems and there is certainly evidence that having sufficient vitamin D levels is needed for us to fight off viral infections and a recent study supports the role of vitamin D in coronavirus infection also. The absolute best source of vitamin D for our bodies is to make it ourselves from the sun. So, how do you know if you are getting enough sunshine (as well as not risking sunburn)?

Calculating how much sun you need to make vitamin D

The amount of vitamin D we make from the sun depends on many factors such as, our age, our skin colour, the time of day, where in the world we are, if we carry excess body fat, how much skin is exposed and whether we are standing up or lying down. Here’s my guide to calculating how much sun you need.

1.     How long is your shadow? We make about 90% of our vitamin D from UVB sun exposure. UVB rays are short and only reach the earth when the sun is directly above us. We can’t make vitamin D in the winter because the sun is at too low of an angle and the UVB rays are absorbed in the atmosphere. A good rule of thumb, therefore is: if your shadow is taller than your height you can’t make vitamin D from the sun. This rule accounts for where you are in the world, the time of day and (of course) if the sun is actually shining! If it is hard to tell whether your shadow is taller than you, you don’t have to lie down on the ground or get out a tape measure…just use a stick held vertically on the ground, mark where the top of its shadow is and then lower the stick to the ground.

2.     Next, does your skin contain some sun-protecting pigment (melanin) already? The darker your skin colour, the less vitamin D you will make (but you will be less likely to burn). Use this chart to find your suggested daily sun exposure time (applies only between 10am and 2pm: if earlier or later, add half as much again). The chart assumes you are wearing a t-shirt and shorts and are lying down.

3.     Make adjustments according to your age (up to 3 times longer is needed for elderly people), if you are overweight (fat tissue stores vitamin D making it inaccessible by the body: up to double the suggested time is needed in this case), if you are standing up (you may need double the time) or if you are in an urban environment where cars are producing pollutants (which block UVB) you may need 2 to 4 times longer.

Alternatively, download an app for your phone, called Dminder, which you can set up to give you a read out of how much vitamin D you have made during your time out in the sun. The app also estimates your blood level of vitamin D, but I would not pay too much attention to that as, in my experience, it is impossible to calculate what anyone’s actual vitamin D level is without testing.

Cautionary notes

Build up to these times though! Don’t risk sunburn: start at only half the suggested time and increase slowly. If your skin shows signs of reddening, skip a day (or more if needed for the redness to subside) and then reduce exposure time until your skin has tanned. As your skin tans, you will need longer, of course. If you are going to be out in the sun longer than these times be sure to cover up or apply sunscreen to prevent burning. Wear sunglasses to protect your eyes when the sun is brightest.

How much vitamin D can you make?

Full-body sun exposure at non-burning levels (i.e., at the times suggested above) can create between 10,000-25,000 IU of vitamin D in your skin. Wearing a t-shirt and shorts will reduce this: to perhaps 3000 to 8000 IU. These doses are much higher than usually suggested for supplementation. Fortunately, you can’t get too much vitamin D from the sun as your body automatically regulates production, whereas vitamin D from supplements can be over-dosed.

How to get more value from your sun exposure

• Having sufficient monounsaturated fats (e.g., in olive oil, avocados) in your diet seems to help vitamin D production.

• Don’t shower immediately after your sun exposure time is up: there is some evidence that vitamin D can be lost if you shower straight away.

• Try to get some exposure daily (weather permitting) as multiplying the above times by 3 in order to get all your vitamin D at the weekend will inevitably lead to sunburn!

Vitamin D and immunity

Vitamin D is absolutely key to many, many body processes (in fact it could more rightly be called a hormone rather than a vitamin), one of which is our immune system.

• Vitamin D is needed for our innate immune system (this is the part of the immune system that can react to new infective organisms rather than the memory side of the immune system that enables us to react to previously encountered threats).

• Vitamin D has an anti-inflammatory action, in that it inhibits several processes involved inflammation.

• Vitamin D is involved in ensuring our body’s barriers (i.e., lungs, gut and skin) are in good repair.

• Vitamin D is needed for creation of the enzymes used by certain immune cells to kill invading viruses and other pathogens.

Thus, vitamin D both improves our ability to respond to disease-causing organisms but at the same time prevents the immune system from over-reacting and causing inflammation.

What if you can’t get enough vitamin D from the sun?

Sadly, as I write these words it is raining so I’ve not been able to make any vitamin D today! Supplementation is likely to be helpful for many clients, but because it is possible to over-do it, I would always recommend testing your vitamin D levels before supplementing. However, the UK Government has recommended that everyone supplements with 400IU daily, year-round.

If you are worried about your vitamin D levels and would like to arrange testing and to discuss appropriate supplementation, please get in touch.