Dog owners are used to inexplicable behavior from their pets; frantic digging in inappropriate locations, barking and howling for no apparent (to humans, at least) reason, spinning or circling in place or even eating their own waste. Certainly, many canine behaviors make no sense to their owners, while the selfsame activities may be perfectly reasonable to dogs. One such behavior is, fortunately, a less energetic and excited one, and that's laying in the sun. We've all seen our dogs pant in hot weather or gulp water after a walk on a summer day. So what's up with dogs laying in the sun? If they overheat easily -- which it seems they do -- then why would they lay in the sun?
The Root of the Behavior
Dogs can and do suffer from heat- and sun-related injuries, just as humans do. Exposed areas of skin, such as the mouth, ears and foot pads can burn if exposed too long to sunlight. And since dogs lack sweat glands, they can easily overheat if not provided with a shady or cool spot to take refuge. And it should go without saying that you should never leave your dog locked in a car on a sunny day, even in mild temperatures. But what draws dogs to sunlight? What appeal does a sunny spot on the living room carpet or in a grassy backyard have for a dog?
The answer is complex, yet surprisingly simple. Just like humans, dogs need exposure to sunlight in order to metabolize certain fats and oils into Vitamin D. That substance is important in bone production and maintenance, and also plays a key role in the body's use of minerals; those are true for mammals, whether human or canine. The only difference is that while humans' Vitamin D is formed in the skin and quickly absorbed, canines' Vitamin D is formed on their fur, where those fats and oils are deposited. As a result, you may notice your dog licking its fur after a sunbath. Essentially, the dog ingests the Vitamin D, just as a human might take a supplement pill.
Speaking of vitamin supplements, it is certainly possible that a dog could produce less Vitamin D than they need, but commercial supplements are available. However, dog owners should be aware that Vitamin D is oil-soluble, meaning that excess D builds up in the body. You can request that your vet add a Vitamin D level test to your dog's regular blood panel testing, and the vet can advise you whether Vitamin D supplementation is needed or even advisable. In most cases, your dog won't need any supplement at all, as long as he is getting regular sunlight. Bear in mind that just sunlight alone isn't sufficient -- for proper Vitamin D formation, you and your dog both need exposure to the ultraviolet B range of sun radiation, often called "UVB" Since most windows block UVB to at least some extent (modern anti-glare and multi-paned windows block most of it), direct sun exposure is better.
Encouraging the Behavior
Left to himself, your dog will probably get all the sunlight exposure he needs on his own. To facilitate that, make sure your dog has a safe and enclosed space to sun himself (a back yard or similar sunny outdoor space is ideal), access to a cooled and/or shady refuge if he gets overheated, and plenty of fresh, clean water. As dogs can overheat and even get sunburns, it is important that you provide your dog an escape from the heat and sunlight as well as providing an opportunity for leisurely sunbathing.
Generally speaking, dogs need considerably less Vitamin D than humans do, and they usually get all they need from good-quality commercial dog food. However, if you want to ensure your dog is getting enough D from natural sources, include wild-caught fatty fish like salmon as well as eggs and organ meats like liver. Dairy products also provide Vitamin D, but not all dairy products are rich in it. Or, even better, find high-quality pet foods that feature those ingredients. You might also want to check the ingredient list to ensure that cholecalciferol appears on it; that's the specific variety of Vitamin D that is most easily and efficiently used by your dog.
Even if your dog is found to have a Vitamin D deficiency, don't give him over-the-counter human vitamin supplements without the advice of your vet. Human supplement doses are far larger than dogs need, and since Vitamin D isn't used up quickly, you can make your dog sick from an overdose. Play it safe by always checking with your vet before giving your dog any kind of medicine or nutritional supplements.
Other Solutions and Considerations
If supplements aren't for you, but you're unable to give your dog proper walks in the sun for whatever reason (e.g. climate or disability), there's still one more solution to explore when it comes to Vitamin D and your dog. That solution is one that folks in extreme northern latitudes of Alaska, Canada, Scandinavia, and Russia have known about for years, and that's UV or full-spectrum lighting. Remember, humans need UVB light to make Vitamin D, too, so if you can't take your dog out in the dead of an Alaska winter, it's apparent that you're not getting enough sunlight, either. You can get UVB and full-spectrum light bulbs, fluorescent tubes and even lamps or "lightboxes" from many manufacturers and distributors, but be sure to check in with both your vet and your doctor before trying this. Excessive exposure to UVB light can cause burns, skin irritation and even eye damage, and those issues can afflict your dog as well as you. Always read the instructions first and get okays from your doctor and your vet beforehand.
While laying in the sun on a pleasant afternoon certainly sounds like a nice way for you and your dog to spend a pleasant afternoon, there's more to it than that. Exposure to the UVB wavelengths in sunlight actually has specific, positive health benefits for you and your dog. And even if doggie sunbathing is difficult or impractical for you, there are some ways around that limitation. Consider dietary supplements or even special UVB lamps, once you've checked the idea with your vet and have had your dog's Vitamin D level tested.