Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease.
Heading into the "Dog Days of Summer" here in August most of us are avoiding the outdoors and the heat as much as possible... and rightly so! However, with most everything in life, sunlight in moderation even during these sweltering days in August is good for us. As humans, we depend on sun exposure to satisfy our requirements for vitamin D. Solar ultraviolet B photons are absorbed into our skin and transformed into previtamin D3, which is rapidly converted to vitamin D3. Season, latitude, time of day, skin pigmentation, age, sunscreen usage, and glass, all influence the production of vitamin D3 in our system. Once formed in our system, vitamin D3 is metabolized in the liver (25-hydroxyvitamin D) before being passed to the kidneys where it is metabolized to its biologically active form (1,25-dihydroxyvitamin D3). Vitamin D deficiency is a very common epidemic in our society, though sadly it is not recognized as such in all too many cases. Vitamin D deficiency not only causes rickets in children (a softening and weakening of the bones), it also precipitates and exacerbates osteoporosis among adults and causes the painful bone disease osteomalacia. Vitamin D deficiency has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. Maintaining proper blood levels of 25-hydroxyvitamin D is not only important for maximizing calcium absorption in the intestines, it may also vitally important for providing the extrarenal enzyme (1alpha-hydroxylase) that is present in most tissue for your body to produce 1,25-dihydroxyvitamin D3.
- Humans make 90 percent of our vitamin D naturally from sunlight exposure to our skin – specifically, from ultraviolet B exposure to the skin, which naturally initiates the conversion of cholesterol in the skin to vitamin D3.
- Few foods naturally contain or are fortified with supplemental vitamin D. For example, an 8-ounce glass of whole milk is fortified with 100 IU (international units) of vitamin D – just 10 percent of what the most conservative vitamin D researchers now say we need daily. In contrast, sun exposure to the skin makes thousands of units of vitamin D naturally in a relatively short period of time.
- While vitamin D supplements are an alternative means of producing vitamin D when regular, non-burning sun exposure is not possible, oral supplementation of vitamin D is not nature’s intended means of producing this vitamin.
- While overexposure to sunlight carries risks, the cosmetic skin care industry has misled the public into believing that any UV exposure is harmful. No research has shown that regular, non-burning exposure to UV light poses a significant risk of skin damage.
- Humans spend less time in the sun today than at any point in human history – which is why more than 1 billion people worldwide are vitamin D deficient.
While it is true that chronic excessive, or burning, exposure to sunlight increases the risk of nonmelanoma skin cancer, avoiding direct sunlight increases the risk of vitamin D deficiency which can lead to even more serious consequences as listed above. Vitamin D Comes From the Sun Sunlight is the best and only natural source of vitamin D. Unlike dietary or supplementary vitamin D, when you get your ‘D’ from sunshine, your body takes what it needs, and de-metabolizes any extra. That’s critical – as vitamin D experts and many health groups now advocate 1,000 to 2,000 IU of vitamin D daily – five to ten times the old recommendations. Because too much ‘D’ from dietary supplements may cause the body to over-process calcium, nobody really knows for sure how much supplementary vitamin D is safe. On the other hand, sunlight-induced vitamin D doesn’t have that problem – it’s the way your body is intended to make it!
|Sunlight Exposure (full body exposure)*||
3,000 – 20,000 IU
|Salmon (3.5 oz. of fresh, wild salmon)||
600 – 1,000 IU
|Salmon (3.5 oz. of fresh, farmed salmon)||
100 – 250 IU
|Fortified Whole Milk, 8-oz. glass||
Source: Holick, MF. Vitamin D Deficiency. New England Journal of Medicine, July 2007
So how do we go about ensuring that we are getting enough vitamin D in our daily lives? You can monitor your serum 25-hydroxyvitamin D concentrations approximately once a year at your physician's office to help reveal vitamin D deficiencies. Or you can simply spend a few minutes a day in the sun. Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 4 or 5 times per week) and increased dietary, and if necessary supplemental vitamin D intakes, are reasonable approaches to guarantee vitamin D sufficiency. We hope that by eating your fresh caught wild salmon that you caught out in the mid-day sun, you can rest in peace knowing that the sun is your friend! Take it easy, 5-10 minutes per day is all it takes to making sure your body has all the Vitamin D you need.