Sunbathing 'boosts men's sex drives': Testosterone levels rise with Vitamin D increase Last updated at 11:58 AM on 02nd February 2010 A spot of sunbathing boosts men's sex drive, reveals a new study. Testosterone levels in men's blood rise accordingly with doses of vitamin D. The vital nutrient is produced in the body after exposure to sunlight and can also be obtained from eating oily fish and meat. Sex boost: Sunbathing can increase testosterone levels in men Researchers at the Medical University of Graz in Austria found men with at least 30 nanograms of vitamin D per millilitre of blood had much more of the main male sexual hormone circulating than those with less. And the average amount of testosterone over the course of the year was subject to the same fluctuations as the vitamin D level. Both decrease from October - at the beginning of the winter months - and reach their lowest level in March because of the weaker solar radiation during this period. Ad Brand, spokesman of the Sunlight Research Forum in Veldhoven in the Netherlands, said: 'Men who ensure their body is at least sufficiently supplied with vitamin D are doing good for their testosterone levels and their libido among other things. The new findings back up previous research that found an hour of sunshine can boost a man's testosterone by 69 per cent. Testosterone is the most important male sexual hormone. In males it is mainly responsible for the development of the sex organs, the formation and maintenance of the typical male sexual characteristics, sperm production and the controlling of male desire. Stimulated by UV radiation, 90 per cent of vitamin D in the body is produced by the skin. An average vitamin D level of 30 nanograms per millilitre of blood (30 ng/ml) represents the scientific value from which vitamin D has a sufficiently positive effect. Optimal values are between 40 and 60 ng/ml.