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エッチ Sex - and Sunlight

Nude sunbathing makes you sexier!

If you turned to this chapter first, I would not want the opening sentence to disappoint you, and in any case it's true. For a number of general reasons, exposure to sunlight is likely to make us feel healthier and improve our sex lives - but there are some very specific reasons also.

The general reasons include a lowering of blood pressure, an improvement in the flow of blood and a rise in the oxygen content of that blood, all of which will stimulate the metabolism within all the tissues of the body.[1] The brain is, without a doubt, the most important sexual organ; without it we would be unable to feel anything physical, emotional or spiritual for anybody else. Anything that improves the blood and oxygen supply to the brain - and sunlight does - can only improve our capacity for loving, both physically and emotionally.

 

エッチ Ultraviolet aphrodisiac

The warm, relaxed sense of welibeing that we obtain from lying in the sun must be one of the closest things on earth to the warmth and security of snuggling up in our mother's arms. Such a feeling cannot be less than beneficial to a healthy sex life, but it seems to go deeper than this. Sunlight is, we now know, essential to health in a variety of ways. Along with protein, calories, vitamins, minerals and all the others, it is an essential nutrient. Sunbathing gives us something we need, particularly nowadays when most of us spend our whole lives indoors; it recharges our batteries. It replenishes our stores of the principal life force of this planet, and so we have more to give to others. It is not for nothing that a caring person is referred to as warm, and an unfriendly or unloving one as cold.

Several years ago I worked in the Solomon Islands, in the Pacific Ocean, just south of the equator. It was regularly remarked upon there that most European couples arrived certain that they had filled their quota of 2.4 children, and never expected to have any more. But two years later many of them left bemusedly clutching a babe-in-arms. The local people said simply that the child was a 'gift belong Solomons'. We pale and sickly expatriates were probably no different from the post that, supposedly dead, is stuck into the ground to support a washing line, and sprouts roots and branches. This was another hazard of Solomon life! There is no doubt that the level of fertility is higher in tropical climates for all living things. Humans are not such an exception as they have always liked to think themselves.

Sunlight falling on the skin can raise the level of sex hormones in the blood. This effect has been known for over fifty years, and has been the basis of, for example, measures to improve the laying rate of hens.[2] But the same thing does happen in humans. When researchers gave doses of ultraviolet to subjects in Boston, USA, they found that a course of five doses, of increasing duration, each of them sufficient to produce slight reddening of the skin, could double the male hormone output.[3]

This ties in with the studies which have shown that levels of testosterone, the major male hormone, rise by about twenty per cent through the summer, reaching a peak in September.[4] In females, the effect was somewhat less but still measurable. The part of the body exposed to ultraviolet also made a difference. Some increase could be achieved whichever area of skin received the irradiation, but while exposing the back produced a doubling in hormones, exposing the skin of the genitals could cause the hormone level to triple.

At this dose level they also found that five treatments was the ideal number. The effect ceased increasing with further exposure. After this experiment, the rise in hormone levels took a fortnight or more to return to normal, and the beneficial impact on health, mental wellbeing and sexuality would of course take longer still to wear off. In other words, a week in the sun can make all the difference.

Naturally, the greater the amount of skin exposed to sunlight or ultraviolet, the larger the effect. Doubling the area of skin exposed will double the amount of UV we can absorb. It is tempting to reflect that the bikini-clad beauty may not be simply attracting male attention by her display of skin - she may also be giving the signal 'my hormones are tanked up and ready for action'!

All this gives us a rather new slant on the phenomenon of the holiday romance. After a week in the sun we feel more relaxed and therefore less inhibited, our sex hormones have been given a boost, and our whole bodies are tuned for reproduction. What's more, the opposite sex instinctively know it.

エッチ Family planning by sunlight

Remarkably, it seems that from birth onwards our sexual development and functioning is subject to regulation by sunlight. In previous chapters we discussed melatonin - the hormone produced by the pineal - which is suppressed by sunlight of sufficient brightness, and which controls the production of hormones by the pituitary gland. One of the substances regulated in this way is LH, luteinising hormone.[5] This is the hormone that causes ovulation and triggers off the second, premenstrual phase of the menstrual cycle. It also appears to influence the development of sexual maturity.

A role for the pineal gland in sexual development was first proposed in 1909 by Otto Marburg.[6] He suggested that the gland produced a chemical that inhibited sexual function, but that with age the production of this chemical would decline as the gland calcified. Since then, melatonin has been shown to suppress sexual function in some laboratory animals. In humans, the LH level is inversely proportional to the level of melatonin. As puberty progresses and body size increases, the level of melatonin decreases to its adult norm, and the level of LH rises.[7] This decline in melatonin cannot be due to calcification of the gland, which normally only happens in middle age or beyond. What does seem to happen is that the pineal produces melatonin at a steady rate over the years of growth, and the increase in body mass causes the melatonin to be progressively diluted and its effect to be reduced.[8]

Nearly all mammals have seasonal variations in their sexual habits, and seasonal cycles of fertility. However, these vary widely from species to species. So do their responses to enviromental light and to melatonin. Put as simply as it can be, mammals can be divided four ways. They are either active during the day (diurnal) or during the night (nocturnal). They are also either monoestrous, which means that they come into season only once a year, or polyoestrous, having regular ovulatory cycles throughout the year, as do humans.

 

エッチ Staying alive

There are obvious survival advantages to timing reproduction carefully. The most important is that if offspring can be born at a time when food is abundant they are more likely to survive - and less likely to threaten the parent animals by restricting their ability to gather food. Viewed in this light, the seasonal variation in mating, and the way this is mediated by changes in day length and therefore in total melatonin production, start to make sense.

Many small animals such as rabbits and hamsters have very short gestation (pregnancy) periods, from two weeks to two months. They mate in the spring and give birth in spring or summer. Reducing the day length, as occurs in autumn, inhibits them from breeding and so prevents them from having babies in winter. On the other hand, sheep and deer have gestation periods of six to eight months, and tend to mate in autumn and give birth in the spring. Therefore a reduction in day length causes them to come into season.[9]

In humans, the peak time for conception is late spring to early summer, leading to birth at the beginning of spring. This is not a very powerful variation, the peak rate of conception being only about ten per cent higher than the annual average.[10] It has also decreased in amplitude throughout this century. But it remains consistent for any given country. In Mediterranean Europe the peak is in April; in France, Germany, Belgium and the Netherlands it is May or June, and in Scandinavia July.

Both luteinising hormone and follicle-stimulating hormone (FSH) - the former definitely suppressed by melatonin, and the latter possibly so - show similar patterns of variation, with a spring and autumn peak in temperate climates.[11] LH also peaks at the time of ovulation, and melatonin shows a drop at the same time, which is clearly not due to sunlight levels, however, but probably to suppression of melatonin production by oestrogen.

Among most species studied, major disruptions of the day/night cycle can interfere with the menstrual or oestrous cycle. In rats, which are nocturnal, continous illumination throughout the twenty four hours suppresses the release of LH and thereby ovulation. In humans, who are diurnal, we would expect light deficiency to do the same. There are no scientific studies yet to show that this is so, but I am not the only doctor to have seen female patients in whom light deficiency appears to disrupt and even completely stop the menstrual cycle, and in whom regular sunlight exposure produces an improvement.

Melatonin appears also to be a major factor in seasonal affective disorder, a recently recognised form of depression, which comes on particularly during the winter months. These patients are very different from the large majority of sufferers from depression, and one of the ways in which they are different is that they tend to have a different seasonal pattern of reproduction, with a peak for starting pregnancy in late summer.[12] This is scarcely surprising - presumably that is the only time they feel fit enough to get pregnant!

In winter, as in shift workers, cholesterol levels are higher. Vitamin D levels are lower, and so are steroid hormone levels. In the spring, however, the sun reappears, and we celebrate the fertility rite of Easter, with chickens and bunnies as its primal symbols, distinct from the more recent Christian ones. Everybody feels and looks better, and therefore more attractive, the conception rate hits an all-time high, the buds come out, and nature's great fertility show is on the road again. If we dare to show our faces out of doors we can join in the fun.


優良エッチだよね　優良エッチ 優良エッチ 優良エッチが見れる　優良エッチしたい

 


Go to Chapter 15
Sparkling Intelligence - Sunlight and the Brain