Health – Sunlight and Physical Fitness

Before the time of Christ, men such as Herodotus and Antyllus believed in the beneficial effect of sunlight in promoting physical fitness. They believed that “the sun feeds the muscles.” The Romans made use of the sun in training their gladiators, for they knew that sunlight seemed to strengthen and enlarge the muscles.

There seems to be conclusive evidence that sunlight produces a metabolic effect in the body that is very similar to physical training. Tuberculosis patients being treated by sunbathing have been observed to have well-developed muscles with very little fat, even though they have not exercised for months.

Beneficial effects which are apparently the same as those of an endurance exercise program can be achieved by a series of exposures to sunlight.

Resting heart rate decreases

It has been demonstrated that after a patient has been on a good endurance exercise program for several months, his resting heart rate begins to decrease (1); it has also been demonstrated that a patient’s resting heart rate will decrease and will return to normal much more rapidly following exercise, if he includes sunbathing in his physical program (2).

Respiratory rate decreases

Similarly, a patient’s respiratory rate not only decreases following an endurance exercise program, but it also decreases following sunbathing, and the patient’s breathing is slower, deeper, and seems to be easier (3).

Lactic acid decreases

Less lactic acid accumulates in the blood during exercise following sunbathing (4) (another effect which usually follows a course of physical training).

Cellular oxygen increases

The ability of the lungs to absorb more of the inspired oxygen (and the ability of the muscle cell to utilize more oxygen) comes as the result of endurance exercises continued for at least several weeks. This means that more oxygen is available for delivery to the muscles while exercising, and to the other body organs while at rest. After fitness has been established through a program of endurance exercises, a marked improvement in the level of energy is noticed. This results in a greatly improved, longer performance in work or play and also allows one to endure stress much better. This whole general improvement in one’s physical condition has come about from an improvement in the circulation and its ability to carry life-giving oxygen out into the tissues.

Sunlight seems also to increase the blood’s capacity to carry oxygen and to deliver it to the tissues. A striking increase in the oxygen content of the blood has been shown to follow a single exposure to ultraviolet light. This effect lasts for many days (5). Severe, intractable bronchial asthma patients were able to breathe freely and the color of their skin returned to a normal pink following an ultraviolet light treatment (6). The blue color of a seriously ill patient suffering from peritonitis, paralytic ileus, and bronchial pneumonia, returned to a normal pink following an ultraviolet light treatment (7).

The mechanism whereby sunlight increases the oxygen content of the blood and its utilization in the tissues may not be the same mechanism by which exercise accomplishes this same goal; but one thing becomes very clear at this point: both exercise and sunlight increase the oxygen in the tissues.

Energy and endurance increase

Fatigue is a common complaint today, but contrary to feelings, more rest may not always be the best answer. As stated previously, a good exercise program decreases fatigue and increases the capacity for work. Marked improvements in one’s endurance and working capacity has also been found to follow sunlight treatments (2). The fact that sunlight seems to increase oxygen in the tissues undoubtedly contributes to this effect. Another factor may be that glycogen (stored energy for the body) is increased in the liver and the muscles following sunbathing (8). This would allow for the increased endurance observed.

Muscular strength increases

Sunlight seems, also, to increase the blood supply to the deep internal organs and muscles (9). The skeletal muscles underlying the skin get an increased amount of blood when exposed to the sunlight (10). This is important in helping to develop muscular strength and will also help to prevent sore muscles when a new activity is undertaken. …

Recently a young male patient consulted me about his elevated cholesterol. Being a muscle builder, he was on a high protein diet and had always believed that a high carbohydrate diet would not provide the building blocks his body needed. When he was told that the ideal diet, for lowering the cholesterol, was a diet low in fat and protein and high in complex carbohydrates, he seemed rather shocked. He expressed his fear of not being able to continue on his muscle building program with this new diet. I told him about sunlight and its cholesterol lowering effect, and how it has been known for centuries to have a muscle building effect. The diet, high in complex carbohydrates with legumes and grains, would have all the protein his body could use in a muscle building program. When I saw this patient several months later and checked his cholesterol, it had fallen by over 30%. He looked well, tanned, and happy, and was enthusiastic about the progress he was achieving as his muscles had increased in strength and bulk on the new program. He was particularly pleased with the fact that he had lost subcutaneous fat. …

Blood pressure decreases

Exercise can be of great benefit in lowering the blood pressure. In one study, 23 men who had high blood pressure were given a moderate exercise program. They did 20 minutes of calisthenics and 30 to 35 minutes of jogging twice a week. After six months on this program, they averaged an 8% drop in their blood pressure (12). In another study, 656 men who had high blood pressure were given a more vigorous program of exercise. It was found that these men had an average reduction in their blood pressure of 15% (13).

A study done at Tulane University, on the effect of ultraviolet light on blood pressure, showed that men, who had normal blood pressure, had a slight lowering that lasted one or two days following a single exposure. At the same time, a group, that had high blood pressure, had a marked lowering of the blood pressure, that lasted five or six days (14). …

Single exposures of a large area of the body to ultraviolet light were found to dramatically lower elevated blood pressure (up to a 40 mm Hg drop). …

It would seem that a good exercise program, combined with a sunbathing program, would go a long way towards eliminating hypertension in this country.

The heart’s efficiency increases

A good endurance exercise program will not only lower the pulse rate, but will also increase the efficiency of the heart, allowing it to pump more blood at each beat, and also allowing the heart more time to rest between beats.

Sunbathing can also increase the efficiency of the heart. In one study, the output of blood from the heart was increased by an average of 39% in the group of patients studied. The increased output continued for five or six days following a single ultraviolet light exposure (14).

Physicians use drugs to stimulate the heart, causing it to pump more blood. These drugs could possibly be eliminated in some cases if the patient were to follow an active exercise program out-of-doors in the sunlight.

Blood sugar decreases

Exercise will lower the blood sugar in a diabetic and enable the diabetic to require less insulin or medication (15). Exercise also helps those with hypoglycemia by stabilizing their blood sugars and keeping them from dropping to the point where they experience alarming symptoms.

Exposure to sunlight appears to have an insulin-like effect in that it causes a lowering of the blood sugar. This is minimal in normal individuals, but dramatic in diabetics (8, 16). When the blood sugar drops in diabetics, it is manifested by a reduction of sugar in the urine. Blood sugar is lowered by a process in which some sugar is removed from the blood and is stored in the muscles and liver as glycogen, thus by increasing its glycogen stores, the human body can reduce its blood sugar.

This process can apparently be achieved by the sun’s stimulating enzymatic reactions in the body. Initially, the sunlight stimulates an increase of the enzyme phosphorylase. Phosphorylase decreases the amount of stored glycogen. After a few hours an enzyme called glycogen synthetase starts to increase. This enzyme increases glycogen storage in the tissues while decreasing blood sugar levels. This effect continues and reaches its maximum level in about ten hours (17).

A high level of glycogen means that the body has enough reserves of energy to supply prolonged physical exercise. From this it can be seen that it would be best to take part in strenuous exercise on the day following exposure to the sunlight. A single suberythema dose (before reddening of the skin) of sunlight produces this effect and it may last several days.

Because of this dramatic effect, a diabetic may need to adjust his insulin dose when he is following a sunbathing program. … Because sunlight combined with insulin can have a very powerful hypoglycemic effect, a diabetic must sunbathe with caution. By gradually increasing the exposure to sunlight and decreasing the dose of insulin, one may avoid a hypoglycemic reaction. A diabetic who chooses to sunbathe should always keep in touch with his physician, who can best determine his need for insulin. …

 Tolerance of stress increases

The psychological effects of training and exercise are beginning to find a prominent place in scientific literature. One study of 60 middle-aged men, showed that after an intensive, four-month physical fitness program, most were significantly more emotionally mature, more self-sufficient, and more imaginative. Others have reported an increased ability to tolerate the stresses of daily life, mood elevation, and ability to sleep and relax; and with this change, came the ability to overcome faulty living habits such as alcoholism and/or cigarette smoking (15).

Those who have had experience with the beneficial effects of sunlight, say that it not only improves the general health, but it also stimulates the appetite, gives a feeling of well-being, and enables one to sleep at night. Somehow, exposure to sunlight has a more relaxing effect upon patients than simply lying down and resting (19). …

One very nervous patient of mine had tried everything to calm her nerves: tranquilizers, vitamins, minerals … . Nothing seemed to work. I informed her of the relaxing benefits associated with sunlight and suggested she try sunbathing following moments of emotional trauma. When next I saw her, she was delighted with the wonderfully relaxing effect of the sunbaths, which far surpassed any benefit she had found from other modes of treatment. …

Sunlight seems to have a relaxing and soothing effect on the stomach and intestines. A research report from Russia shows that duodenal ulcers are greatly improved after a course of sunlight treatments and can also be prevented from reoccurring (21).

Sunlight and exercise better than exercise alone

The fear of heart disease may be the major motivating factor in stimulating people to exercise – and for good reason. It has been known for some time that exercise “converts abnormal electrocardiograms to normal ones” (22, 23). And a study of the results of combined sunlight and exercise, showed that a group that was getting the sunlight treatments with exercise, had improved almost twice as much, as shown by their electrocardiograms, as had those who only exercised, even though both groups were on a general health resort treatment program (24). …

There is some evidence in the scientific literature that sunlight can increase the energy level in human cells (28). This could explain some of the increased physical fitness that comes with exposure to sunlight. Certainly sunlight is the source of energy for the entire plant kingdom and man may also derive direct energy from the rays of the sun. …

It should be emphasized that, in order to achieve the training effect associated with exercise, a gradual and consistent exercise program must be maintained over a period of months. To achieve this “training effect” from sunlight, a similar gradual and consistent exposure to sunlight must be maintained. …

How to sunbathe

One should always consult his physician before beginning a sunbathing program. He can best evaluate your particular needs and possible problems.

One’s sensitivity to sunlight is the first deciding factor. … Some can spend hours during the summer out-of-doors and not become sunburn, while others can spend only a few minutes. Many drugs, cosmetics and soaps can so sensitize the skin that burning becomes a real problem. Generally, blonde, and red-haired people need to begin with brief exposures, and will require less total sunlight than do brunettes because the light can pass more readily through lighter skin. Dark-skinned people can spend more time in the sun initially, and then they will need to increase their exposure time, because sunlight does not readily penetrate dark skin. …

As to how much time to sunbathe, it really comes down to a program that varies with individuals. The best way to start is by experimenting, perhaps 2 minutes on each area – front, back, right, and left side – in full summer sun, then gradually increase the exposure on each area by, one minute or longer every day. If you turn slightly pink several hours after the exposure, hold the time steady for several days and then start again increasing the exposure time. It is best, when starting, to keep the time lower than necessary rather than longer and experiencing a burn. Never burn! The circumstances and the situation certainly will dictate how much skin can be exposed while sunbathing. …

The time of day, season of the year, and latitude are all important when considering how much time to sunbathe. Elevation also plays an important part, for sunburning can take place faster at a higher elevation than it can at sea level. The amount of ultraviolet light reflected from the environment can also make a big difference. Snow will reflect about 85% of the ultraviolet, dry sand 17%, and grass 2.5%. Water is a poor reflector of ultraviolet light, contrary to public opinion. …

In most temperate climates, it is possible to sunbathe year around if you get out of the wind with no air movement over your body. On bright, sunny winter days it is a fabulous experience to lie in the warm sun. … Most of the beneficial effects of sunlight can be obtained without turning the skin red, so even in northern areas, winter sunbathing can be helpful. …

During the summer, it is preferable to sunbathe earlier in the day while the air is cooler, because sunbathing can become uncomfortable as well as dangerous during the heat of the day. … If one feels himself becoming too warm, he should move to the shade or take a lukewarm shower. … One should not be afraid of sweating, as the sweating process cools the body and eliminates toxins, and the sweat contains substances that can absorb some of the sun’s burning rays. …

No kind of cream or lotion should be applied to the skin while sunbathing. Clear skin is the best (skin washed with plain water to remove soap films and cosmetics). Fat or oil applied to the skin will stimulate the formation of cancer cells. Most of the suntan creams, butters, and lotions have fat as their base and should not be used. …

If one burns easily, get out of the sun sooner; season yourself by graduated, day by day exposure. Used moderately, sunlight will give the skin a soft, velvety-smooth feel along with a healthy glow.


1)     Skinner, J. S., Holloszy, J. O.; and Cureton, T. K.: Effects of a Program of Endurance Exercises on Physical Work, Amer J Cardiol 14:747, 1964.

2)     Lehmann, G., and Szakall, A.: Der Einfluss der Ultraviolettbestrahlung auf den Arbeitsstoffwechsel und die Arbeitsfahigkeit des Menschen, Arbeitsphysiologie 5:278, 1932.

3)     Laurens, H.: The Physiologic Effect of Ultraviolet Radiation, JAMA 11:2385, 1939.

4)     Parade, G. W., Otto, H.: Alkalireserve und Leistung, Z Klin Med 137:7, 1939.

5)     Miley, G.: Ultraviolet Blood Irradiation: Studies in Oxygen Absorption, Amer J Med Sci 197:873, 1939.

6)     Seidel, R. E, et al: Preliminary Report of Results Observed in Eighty Cases of Intractable Bronchial Asthma, Arch Phys Ther 24:533, 1943.

7)     Miley, G.: Ultraviolet Blood Irradiation Therapy in Acute Pyogenic Infections, Amer J Surg 57:493, 1942.

8)     Pincussen, L.: The Effect of Ultraviolet and Visible Rays on Carbohydrate Metabolism, Arch Phys Ther X-ray Radium 18:750, 1937.

9)     Levy, M.: Der Einfulss Ultravioletter Strahlen auf die Inneren Organe der Maus, Strahlentherapie 9:618, 1919.

10)   Bing, H.I.: Effects of Ultraviolet Rays in Depth and Duration, Acta Med Scand 114:217, 1943.

12)   Boyer, J., and Katsch F.: Exercise Therapy in Hypertensive Men, JAMA 21:10, 1970.

13)   Hellerstein, H. K.: “A Primary and Secondary Coronary Prevention Program,” in Raab, W. (ed.): Prevention of Ischemic Heart Disease, Springfield: Charles C. Thomas, 1966.

14)   Johnson, J. R., et al: The Effect of Carbon Arc Radiation on Blood Pressure and Cardiac Output, Amer J Physiol 114:594, 1935.

15)   Cooper, K. H.: Aerobics, New York: Bantam Books, 1968.

16)   Ellinger, F.: The Biologic Fundamentals of Radiation Therapy, New York: Elsevier Publishing Co., Inc., 1941.

17)   Ohkawara, A., et al: Glycogen Metabolism Following Ultraviolet Irradiation, J Invest Derm 59:264, 1972.

19)   Lorincz, A. L.: The Physiological and Pathological Changes in Skin from Sunburn and Suntan, JAMA, 173:1227, 1960.

21)   Okhonko, V. I.: Treatment of Duodenal Ulcer with Cholinolytics and General Ultraviolet Radiation, Vrach Delo 1:61, 1976.

22)   Mikhailov, V. A.: Influence of Graduated Sunlight Baths on Patients with Coronary Atherosclerosis, Sovet Med, 29:76, 1966.

23)   Kidera, G. J.: Exercise Aids in Converting ECG to Normal, JAMA, 204:31, 1968.

24)   Goldman, A. N., et al: Effects of Continuous and Impulse Ultraviolet Radiation Therapy in Clinical Health Resort Treatment of Patients with Hypertension and Chronic Coronary Insufficiency, Vop Kurort Fizioter 36(5):417, 1972.

28)   Kabat, J., et al: Effect of UV-irradiation of Shifts of Energy-rich Phosphate Compounds, Zabl Bakt Hyg I Abt Orig B 162:393, 1976.

Sunlight, Zane R. Kime, M.D., M.S., 33–47, 237–245.