Sunlight for House Dogs

chihuahua dog with sunglasses and a sun hat on the beach, bathing in the sunlight


Do Dogs Need Sunlight?

From toy dogs to giant breeds, many fanciers keep their show dogs as housedogs. While this is emotionally preferable to being kept outside, 24/7 confinement inside is unhealthy for canines.

Nature designed all mammals, excluding rodents, to spend most of their waking hours in sunlight. Surely you’ve noticed your cat stretched out on the window sill? Your house dog basking in the sunlight streaming through the window? Probably it is the only window that isn’t covered by drapes, blinds, or mechanical shutters.

As an aside, the importance of sunshine for humans has been lost in the push for antidepressants. Sunlight is free. Pills are profitable. There are numerous medical reports on the health problems of office workers due to sunlight deprivation but the most notable effect on night workers/day sleepers is emotional-mental problems.

Sunlight regulates estrus cycles. Sunlight deprivation equates to reproductive problems. Whether you are trying to start a family, a hobby breeder or dog show exhibitor, you need to be aware of the damaging health effects of sunlight deprivation. So here’s the point. Nature knows best. Mammals weren’t designed to live indoors—or wear sunglasses—so let’s just stick to simple science and how it should affect the way you “house” your dogs.

Consider the oldest “American” breed, the Chihuahua, which is behind all toy breeds. I know, it is hard to comprehend a wolf and the Chihuahua as related but they are. The Chihuahua originated in the southern hemisphere desert, i.e. long hours of direct sunlight. Thus the natural color of the Chihuahua is a light-reflective white or light tan. The wolf originated in the northern hemisphere some 20,000 years ago and the predominant coat color is dark to gather warmth from weak sunlight.

Reproductive problems are convincingly common in house dogs as compared to puppy mills or mutts. Why? It has nothing to do with purebred genetics. It is environmental. Most mutts, hunting, or working dogs are outdoors in the sun. And equally important, they are not inundated with artificial light after dark.

Everyone knows sunlight, nature’s blessing of vitamin D, prevents crooked or weak bones but did you know that light deprivation prevents normal ovulation? Cat breeders will tell you both sexes need natural sunlight in order to produce kittens. So, if you’re building or planning a kennel, include large windows and/or skylights. If you’ve already built that dream-kennel, change to full spectrum lighting and turn the lights off at night!

Science behind sunlight, thyroid gland and normal reproduction cycles. Light enters through the iris and transmits to the pineal gland which then signals the pituitary, thymus and thyroid glands. Every experienced breeder knows about thyroid deficiency and its effect on ovulation but the pineal gland also plays a master role in the immune system’s ability to respond to virological or environmental challenge.

Melatonin (a master hormone) works in the hypothalamus region of the brain during darkness. When we keep dogs inside in prolonged artificial lighting, it prevents tissue regeneration and the production of serotonin. Serotonin helps to work neurotransmiters, stabilize homeostasis, and maintain connective tissues! Melatonin also suppresses the development of tumors and may actually reconstitute bone marrow integrity.

So we have two things going on. Litters born and raised indoors receive inadequate sunlight. Conversely, bright glaring light is the last thing newborns should experience. All felines and canines are born in a darkened place—under the house or the back of the barn. When the eyes have opened and adjusted gradually to natural degrees of sunlight, from dawn, to midday, to dusk, the babies emerge from the nest.

Here’s a thought for you. All carnivores are born with eyes closed and are unable to walk. When their eyes open, predators can toddle out into the sunlight, just when they need it to insure strong bones, joints and maximum development. Still thinking? Herbivores (deer, horses, cows, etc.) are born with eyes open and can run within minutes of birth!

While your brain is processing that non-puzzle, know this – NIH has stated “laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers” and subsequent studies associated a higher calcium and vitamin D intake with a lower incidence of colon cancer. Vitamin D from natural sunlight may also help protect against prostate cancer, which is becoming more common in dogs. There are over 200 PubMed articles on vitamin D as it relates to the prevention of cancers, type 1 diabetes, heart disease and osteoporosis.

Sunlight’s benefits and the adverse effect of artificial light have been suppressed by commercial interests but now you know why puppies should sleep in darkness and play outside in sunlight.

Excerpts from the author’s 2007 AKC Gazette Column, “Toy Breeds and Light”
From the monthly column “On The Line”. Showsight September 2019 Issue. Click to subscribe.


  • Barbara “BJ” Andrews is the breeder of over 300 AKC Champions including over a dozen All-Time record holders. She is the author of 8 breed books and founder of 3 AKC Breed Clubs. In 1998 she launched the world’s first public website ( followed by and which, as part of the NetPlaces Network, serves all facets of dog ownership and exhibition. She and husband Bill pioneered the Akita, Miniature Bull Terrier, and Toy Fox Terrier to AKC recognition and BJ served on the board of each Parent Club. She has judged in England and AKC Specialty Sweeps. She was awarded UKC All Breeds approval but has never applied for an AKC judges license because it could interfere with objective reporting on the sport.

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