Young fathers: It is best to sow in winter

Author: Han Fei (Center for Excellence in Molecular Plant Sciences/Institute of Plant Physiology and Ecology, Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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Parents who want to have a baby will think about the question "Which season is the best to have a baby?" Of course, in addition to the Buddhist preparation for pregnancy, some people believe that "a year's plan begins in spring", and the spring is warm and the flowers are blooming, and some people believe that it is better to conceive in summer, so that when the child is born, the mother will have a sufficient supply of fruits and vegetables. In addition, there is a view that babies conceived in autumn and winter will be smarter.

However, these have no strict scientific basis.

Now, there are a few weak scientific reasons to support the idea that sowing is best done in winter.

Figure 1 Cold "tempering" of stallions, Image source: Heilongjiang Daily, photo by Jia Weiyuan

Will it be easier for a baby to get fat if conceived in winter?

A paper published in Nature Medicine found that if women conceive in winter, their children will be less likely to be obese (they will have more brown fat in their bodies, which is responsible for consuming energy and producing heat), and their energy metabolism efficiency will also be higher when they grow up.

Therefore, the claim that babies conceived in winter will be healthier in the future has successfully received "academic endorsement" from the Swiss Federal Institute of Technology. The team led by Christian Wolfrum found that:

Adult Swiss who conceived between October and February of the following year had relatively high levels of brown fat and relatively low BMI. Those who conceived in the summer had significantly lower levels of brown fat and a relatively higher obesity rate. So far, it seems that a simple conclusion can be drawn: the best season for sowing is winter, followed by early spring (outdoor temperature around 0°C).

Figure 2 PET/CT scan shows that thin people in cold conditions have more brown fat in their shoulder blades and other areas. Image source: https://herbscientist.com/get-healthy-live-longer-with-cold-thermogenesis/

Moreover, scientists have provided more evidence.

They first let the two groups of mouse fathers stay at room temperature (23°C) and low temperature (8°C) for a period of time, and then reproduced separately. After the mice were born, they studied their brown fat content and energy metabolism under low temperatures.

The results are obvious. The offspring of rat fathers who have been "trained" in low temperatures are healthier, with more brown fat and beige fat (more white fat makes people fatter, but more of these two types of fat makes it less likely to get fat). At the same time, their metabolism is more active in low temperatures, so their body surface temperature is also higher.

Figure 3 P-CE represents the offspring of the mouse father who was exposed to cold. After 30 hours of exposure to the cold environment, the body surface temperature is still very high (because the content of brown fat, the heat generator in the body, is higher). Image source: Reference 3.

What is the reason for this?

The answer lies in sperm. Sperm is afraid of heat, so the testicles and scrotum are both outside (there is also a theory that the testicles hanging outside extend the "runway" of sperm during fertilization, which is more conducive to selecting the best sperm). Scientists performed methylation sequencing on the sperm of volunteers and found that low temperature caused fluctuations in the transcriptome level of brown adipose tissue cells, which in turn changed the methylation level of sperm.

It must be said that eggs from the mother will clear the methylation marks beforehand and then re-methylate them as needed, which is why Christian Wolfrum's research focuses specifically on fathers rather than mothers.

In short, the final result is that the sperm from the father "remembers" that it is "cold" outside and needs to produce more heat to resist the cold. In this way, when the fertilized egg injected by the sperm grows up, his body also works according to this "teaching": most of the excess heat taken in is dissipated in the form of heat energy through brown fat and beige fat.

Figure 4 Brown fat is found between the shoulder blades, on the back of the neck, in the armpits, in the mediastinum, and around the kidneys. It is highest in infants and young children and then gradually decreases with age. Image source:

https://quizlet.com/9417017/ecological-terms-sci-523-flash-cards/

It’s not over yet.

Life transmits "past life memories" through epigenetic modifications, such as methylation. For example, a tree lets its descendants know that the environment is dry, etc.; for another example, how do plants remember to bloom in spring from generation to generation? The answer is that the VALs transcription factor activated by low temperature puts methylation caps on the flowering regulatory factor FLC, making them silent, and the flowers bloom; when the weather warms up and the flowers bloom and fade, the Pioneer transcription factor wakes up FLC (demethylation), and finally realizes "apple trees no longer bloom in autumn, and everything has its time."

Similarly, the "past life memory" of human paternity can be passed on to offspring through epigenetic modification. Therefore, the responsibility of prospective fathers is even greater. For example, studies have shown that if he gains weight six months before seeding, the obesity information will also be recorded in sperm through methylation, making the baby more likely to gain weight in the future, thus increasing the risk of various metabolic diseases.

A few small questions

1. This kind of research really requires a lot of thought! Is it necessary?

A: Yes. In fact, it is a kind reminder to prospective fathers: bad living habits (obesity, long periods of sitting/stifling heat/staying up late leading to decreased sperm quality, smoking, alcoholism) will be recorded as epigenetic modifications, burying safety risks for future generations.

2. Do I need to soak it in ice water beforehand?

A: You have misunderstood. Just like plants need to be exposed to low temperatures for a long time (one autumn + one winter) to bloom, low temperatures also need a long time to modify the epigenetic changes of sperm.

Figure 5 Image source: https://bengreenfieldfitness.com/podcast/biohacking-podcasts/cold-thermogenesis-how-to/

3. My son was conceived on Christmas. Why does he like to eat vegetables and is round when he grows up?

A: There are multiple causes and genes for obesity. This paper found a way for the body to avoid obesity. Without it, fat people will get fatter... (take it as such).

4. The expectant father needs to pay attention, but the expectant mother doesn’t care?

A: No. Another paper in Science Advances pointed out that the nutritional status of expectant mothers before and after conception can significantly affect the epigenetic marks of MEs (metastable epitaxial alleles) in the child's genome, some of which may increase the risk of cancer and obesity in the child in the future.

References:

Zeng Tao et al., Embryonic epigenetic reprogramming by a pioneer transcription factor in plants, Nature, 2017;

Noah J. Kessler et al., Establishment of environmentally sensitive DNA methylation states in the very early human embryo, Science Advances, 2018;

Weifei Sun et la., Cold-induced epigenetic programming of the sperm enhances brown adipose tissue activity in the offspring, Nature medicine, 2018.