That vitamin D deficiency is a growing epidemic across the world, and is contributing to many chronic debilitating diseases, including  cancer, is already an established fact.  

What’s surprising is that you may be deficient even if you live in places like Hawaii, or the Caribbean, where there’s no shortage of sunshine. I just returned from Maui where I spend my winters, and I saw many local residents there that were seriously deficient in vitamin D.  

If you live in one of these perpetually sunny environments but work the entire week indoors and don’t make a conscious effort to go outside during the weekends you will become vitamin D deficient.  It is simply not enough to walk from your car to work and home and expect to get enough sunshine. 

Your windows also screen out the vast majority of UVB from the sun shining through, so you will NOT generate significant levels of vitamin D by sitting in front of a sunny window. There are other benefits to doing that but generating healthy vitamin D levels is not one of them. 

So since most of us live in more temperate climates where we have to be very careful about getting enough sunshine, what are the factors we need to be aware of to maximize vitamin D production? 

Factors That Influence Production of Vitamin D in Your Skin 

The reason for this is because production of previtamin D3 in your skin is highly individual and varies depending on several factors, including:

• Skin color, and current tan level
• Amount of time spent in the sun
• Weather conditions such as: cloud cover and pollution, ozone layer, surface reflection
• Latitude and altitude (elevation)
• Season
• Time of day
• Use of sunscreen
• Clothing

So, let’s review these factors to see how they affect your production of vitamin D when you’re trying to metabolize it naturally, from the sun, as opposed to getting it from an oral vitamin D supplement.

Skin Color, Current Tan Level, and Amount of Time Spent in the Sun

Caucasians and others with paler skin will hit an “equilibrium point” after about 20 minutes of exposure to UVB light, at which point vitamin D will no longer be produced.  

You can tell you’ve reached your optimal exposure for the day when your skin turns a very light shade of pink. After that you’re only increasing your chances of getting burned, which is something you definitely want to avoid.  There is NO additional benefit to staying in the sun any longer. You only risk damage by extending your time in the sun.   

It’s not like your gas tank. Your body can only produce a limited amount of vitamin D every day. Once it reaches its limit you only cause damage by going beyond that amount.  However, once you have a tan you spend much longer in the sun. 

If you have darker skin, reaching this equilibrium point can take two to six times longer (or up to an hour or two), depending on your pigmentation. 

A light-skinned person fairly far from the equator (such as in the UK or the northern U.S.) needs at least three of these 20 minute sessions per week, in bright midday sunlight and with few clothes.  

A dark-skinned person, of course, should be outside significantly longer, and more often, to get the same effect.  

Weather Conditions 

The more clouds there are, the less UV radiation reaches the earth’s surface. However, UV can penetrate cloud cover to some extent, so it is still possible to get sunburned on a cloudy day. This is especially true under light clouds, which can block infrared radiation but not UV radiation, leaving the day deceptively cool. 

Likewise, some types of ground cover reflect UV radiation, increasing its intensity even in deceptively shaded areas. These surfaces include sand, snow, and water. 

Air pollution, on the other hand, can block UV radiation too effectively. If the air pollution contains large amounts of ozone, UV penetration can be reduced to a sometimes dangerously low level for at-risk populations. This can be particularly true of cities surrounded by hills or mountains, which trap air pollution. 

Latitude and Altitude 

Sunlight is, of course, strongest at the equator, where the sunlight comes from directly overhead rather than at an angle; the solar radiation therefore has the shortest distance to travel through the earth’s atmosphere. The UV radiation is about four times as strong at the equator as it is at the Arctic and Antarctic circles. 

To find the latitude of your town or city, check out this easy-to-use International Latitude / Longitude finder to determine how your latitude affects your sun exposure: 

• Between 0 and 10 degrees latitude, there is very intense sunlight for several hours before and after noon, year-round. Pale or untanned skin will be completely overwhelmed in just a few minutes.
• Between 10 and 30 degrees latitude, there are several hours of very strong sunlight each day, especially during the summer, but the hours after dawn and before dusk can be milder.
• Between 30 and 50 degrees latitude, sunlight can be strong during the summer, but a tan can be built up gradually by starting in the milder spring.
• Upwards of 50 degrees latitude, summers are often short. However, the inhabitants of these countries often have pale skin that should still be exposed to summer sunlight with care. Anyone with very dark skin living at these latitudes is at a very high risk of vitamin D deficiency. 

UV radiation is also more intense at higher altitudes, because there is less atmosphere to absorb it. The radiation increases by about 10 percent for every additional mile above sea level. You will therefore burn more easily when you’re at high altitudes -- a fact that is often difficult to remember because it is usually colder at higher altitudes.  

Season 

Always start “priming” your skin early in the spring when the sun’s rays are still mild. In summer, avoiding being outside when the solar radiation is at its most intense is a good idea at most latitudes, to avoid sunburn. 

In many parts of the world it is even possible—and probably advisable—to sunbathe at noon in the winter with as little clothing as the weather permits  (finding a place that is out of the wind can reduce the cold significantly). This is the time of year when you need to be most concerned about the amount of vitamin D you are receiving, as your vitamin D levels can drop by up to 50 percent during winter months. 

Time of Day 

UV levels are at their most intense at noon. This is because when the sun is directly overhead, it has the least distance to travel through the atmosphere before reaching the earth’s surface.  

You’re better off sunbathing during the off-peak hours: before 12 noon or after 3 pm. 

Use of Sunscreen and Clothing

In some societies where clothing traditionally covers most of your body year-round, a greatly increased risk of rickets and osteomalacia have been observed. You do need to expose large portions of your skin to the sun, and you need to do it for more than a few minutes.

Keep in mind that using sunscreen while outdoors in large part nullifies your efforts to metabolize adequate amounts of vitamin D. I recommend testing your vitamin D levels to make sure you're not deficient before resorting to sunscreen of any kind. 

But, if you really need some form of sun protection because you’re outside for extended periods of time, either use light clothing to cover exposed areas, or look for safer, natural sunscreen products that contain no petrochemicals, which you can likely find in your local health food store.  

Another excellent resource is the EWG's "Skin Deep Report," where you can find out which brands of sunscreens are free from toxic chemicals.

How To Protect Yourself Against Sunburn Without Toxic Sunscreen

The amount of antioxidants you get from your diet plays a major role in helping you avoid sunburn. The more antioxidants you have in your skin, the lower your risk of getting burned. They actually act as an internal form of sunscreen, allowing you to maximize your exposure while lowering your risk of negative consequences.

Foods containing effective antioxidants include whole fresh vegetables and fruits such as goji berrite (not the juice), raspberries, blackberries and blueberries.

Vitamins A and C are also vital as your cells use these vitamins to regulate both light absorption and protection against overexposure. Since you want to expose at least 40 percent of your body to sunlight for up to an hour (or more) each day, making sure you have this built-in protection against burning too quickly can be quite helpful – especially if you’re very light skinned.