#29 Is it a coincidence that a female's menstrual cycle is equivalent to the moon's orbital period? Are they connected?

This question comes from Tom S. via the blog.

There are a couple things in this question I want to address. First, if it is a coincidence it is not connected. In science there is a concept of "coincidence or correlation does not imply causation or connection". There is a great humor blog called Spurious Correlations that shows that you can make anything correlate.

That aside, the second and more important concept to address is that this assumes all women have the same menstrual cycle. This is an assumption that is often made but not reality. What it comes down to is that this concept is comparing two estimates as if they are real, measured and accurate numbers. I think this is what we will address, as well as the moon cycle itself.

How long does it take the moon to orbit the Earth?

This in itself is a complicated question because the moon phase appearance is influenced by the moon orbiting the Earth and the Earth orbiting the Sun. The moon orbits the Earth in just over 27 days. However, it is 29 and a half days for the moon to pass through all the phases. (Discussion of Lunar cycles) Which of these would we consider the moon cycle? The 28 days we usually hear is an average of these two time lengths. (We will see in this discussion that a lot of common knowledge on the subject is based in comparing multiple averages and not real numbers.) In truth, every common calender lists the moon cycle as 29.5 days and not the 28 that we associate with the menstrual cycle. You can read about all the calender relations and much more on lunar cycles here.

The female cycle

There is a huge misnomer in common knowledge that a female cycle is fixed at a certain number of days. This is not true. The length of a female cycle changes for many reasons and may change over a woman's life time. To this discussion I think it is important to look at some of the many things that can change the length of a woman's menstrual cycle. Most women fall in a 21 to 35 day cycle while it is not uncommon for women to exceed the 35 days as well. This time period is for the average woman without the influence of medications, such as birth control, or other influences from the list we will be discussing below. Of those 21-35+ days, 2-7 days is spent bleeding. This is the numbers for adults. However, for teens and pre-teens the range is even greater and may be 21-45 days or longer between periods.

Circadian Rhythm and Sleep

Our natural internal rhythms can alter the frequency and duration of a menstrual cycle. Sleeping excessively or not enough can have an impact on menstrual cycle length. Chronic insomnia can affect the length of a menstrual cycle causing a woman's normal cycle to be longer than the 35 days at the upper end of the average. Melatonin levels can change the length of a cycle too. This is important because of the use of over-the-counter melatonin for sleep which makes this influence more common than in the past. There is plenty of research that shows sleep rhythms can have such an effect on the cycle that it can impact fertility.
A research paper about circadian rhythms and menstraul cycle

Eating and Weight

The amount one eats can impact length of menstrual cycle. Decrease in food due to starvation, be it external such as famine or internal such as anorexia or bulimia, can  decrease the frequency of menstrual cycles. In some cases lack of food can eliminate the menstrual cycle completely. On the other side, over eating and being obese can decrease frequency of menstrual cycles. Types and quality of food can also affect menstrual cycle duration. Other things such as alcohol and caffeine consumption can alter period length.
Research paper weight and sex-hormones
Research on anovulation
Bariatric surgery and menstrual/fertility issues

Exercise

Intense exercise can alter fertility and menstrual cycles as well. Called exercised induced Amenorrhea, this is a complete lack of menstrual cycle but it can also be a decrease in frequency.

Medications and Illness

A large number of illnesses can affect period duration. Everything from anemia to uterine cancer can alter menstrual cycles. Medications can also affect the duration and intensity of menstrual cycles. Many mood stabilizing medications such as anti-depressants can increase or decrease the length of menstrual cycles.
Diseases and conditions that are effected by or affect menstrual cycles.

Age

Young and old women both experience irregular menstrual cycle lengths. Between the ages of 25 and 40 women experience the most regularity in periods. Prior to the age of 25 menstrual cycle irregularity is related to the hormone imbalances related to sexual maturity and development. After 40 the irregularity is due to peri-menopause.

Stress Levels

High stress levels can trigger less frequent or erratic menstrual cycles. At the root of this is the body mechanism, the same one in play with starvation, that signals that this is a poor time to conceive a child.This body stimulus can reduce the amount of menstrual cycles, which reduces the number of ovulations or chances to become pregnant.
Stress and Menstration
Affects of stress on women's health
Research paper on job stress and menstrual length

Other considerations.

The often cited study by Winnifred B. Cutler in 1980 that is used as proof that women's cycles are related to the moon doesn't prove anything. In the study it was shown that 40% of the studied women had a period start within 2 weeks of the full moon, i.e. within half a month of the full moon. The two week time frame is very large considering this is half of the entire moon cycle. The other thing to consider is most of the women, 60%, showed no relationship at all with time of period and full moon.

More reading:

Exercise and weight and menstrual cycles
Missed periods, exercise and osteoporosis
Stress, ovulation and bone health
List of everyday things that can affect periods.
Causes of Amenorrhea
The moon and activities
Moon cycle length and estrus length in multiple animals.
Do women who live together actually synchronize?

Question #27 What is the importance of herd immunity?

From Linda on Facebook.

Before we talk about the importance of herd immunity we should define it. Herd immunity is sometimes called community immunity. I think herd immunity is most easily defined through an example.

Let's imagine two communities of 100 individuals. 

Community A Most of the individuals have had vaccinations (90) and there are 10 people who are either too young or too immune compromised to be vaccinated. So in this community 90% of people have vaccinations and 10% cannot receive them.

Community B Few individuals have had vaccinations (10) and there are also 10 people in this community that are either too young or too immune compromised to receive vaccinations. In this community 10% have vaccinations, 10% are unable to get vaccinations and 80% are unvaccinated, meaning they have no immunity.

Now, let's imagine the virus that the vaccination is for comes into contact with these two communities. 

In community A, 90% of people who come into contact with the virus are not effected by it because their immune system has antibodies. These 90% of individuals also do not become carriers, meaning once they come in contact with the virus they do not carry the virus off to infect other people. This means that 9 out of 10 times the virus tries to invade this community it is ineffective because of the immunity. Most of the herd/community is immune to the virus so those who don't have the immunity are unlikely to contract it.

In community B, 10% of the people who come in contact with the virus have immunity and do not become sick or carriers. However, 80%, or 8 out of 10, of individuals do come down with the sickness and carry the virus into the community to infect others. That means the 10% unable to be vaccinated have an 80% chance of catching this virus. Those most susceptible to the virus are highly likely to come in contact with a community member who is carrying the virus.

This is the basis of herd immunity, the more of the herd that is immune the more safeguard there is for those who are unable to receive vaccinations or may be in serious danger from becoming sick, such as the young, those with immunodeficiency diseases, or undergoing chemotherapy. Herd immunity works on small scales; a single family with a new baby or a sick elder; or a community as large as an entire city, state, country or the broader world. Herd immunity is important to stop the spread of a disease from one individual to another and is a major force in preventing epidemics and pandemics.

What percentage (R0) of the population must be vaccinated to provide herd immunity?

This is a very tricky question and involves several variables. One major variable is how contagious the virus or bacteria, or how fast it spreads. The more contagious the disease the higher the percentage of people needed to provide herd immunity. The interaction and travel patterns of the community matters to this as well. With modern travel, such as cars and airplanes, someone carrying a virus can travel much farther in a single day. This means that the herd immunity of the home population and the destination population are both equally important when it comes to a carrier. In general, the higher the percentage who are vaccinated, the better the herd immunity.(Check out the link in the more information section for an article about how this is calculated)

Why are vaccinations important to herd immunity?

Vaccinations provide a few important things. First, immunizations create a record of who has immunity. This information is important during an outbreak and also allows officials to track down patient Zero. (Patient Zero is a term for the person who initially brings a disease into a community. Knowing patient zero can allow officials to track who they have been in contact and who might have contracted the illness.) Secondly, vaccinations allow the individual and the medical professionals to know that an individual, or group of individuals, is immune to a specific strain of a disease. Perhaps the most important aspect of herd immunity through vaccinations is that it allows a large portion of the population to become immune without having to contract the disease. This is a particularly important benefit when the disease is debilitating or has a high rate of death, such as polio. A final importance, at least to those who have and love pets, is that some diseases are zoonotic, meaning they can be transmitted between people and animals. Having a pet and/or person vaccinated against a zoonotic disease protects the human population, the pet population, and in some cases populations of food animals.A great example of a pet vaccination that provides safety to both the pet and the humans who love them is the rabies vaccination.

More information:
Research paper on the benefits of herd immunity in Meningitis
 PBS page that discusses how to calculate percentages required for herd immunity to be effective as well as other related topics.
CDC discussion of herd immunity
Series of interactive animations to show visually the impact of herd immunity vs no herd immunity

Free Courses online that cover immunity and health
An Introduction to Global Health
An Introduction to Population Health
Epidemiology: The Basic Science of Public Health
Epidemics, Pandemics, and Outbreaks

#19. This will make your skin crawl....

I am both repelled and fascinated by parasites, particularly those that effect and can be seen on and in the skin. So this post is dedicated to a discussion I had about parasites and sharing some of the ones that really creep me out.


The Bot Fly, or warble or gadfly, are flies that lay their eggs in the skin of the host (or some grow in the stomach). These larvae then eat the flesh and poke out holes to the surface for gas exchange. Eventually, they will climb out. While they are truly skin crawling they do not cause permanent damage or death to the host. One of the most ick inducing infestation, IMHO, is the botfly incubating in the human eyelid.
How botfly maggots are extracted.


Scabies, from the Latin word "to scratch or itch". This is a small mite that infests the skin. Scabies mites burrow into the skin and then live there in burrows. There are several times of scabies, each with their own infestation and spreading rates. Norwegian or Crusted Scabies is the worst causing crusts of skin under which the scabies colony lives. This is also one of the most contagious forms as it causes the most intense scratching. Scabies is not deadly, in most cases, and can be treated with medication. From the CDC.

A delightful illustration of the scabies mite in the skin.

 Screwworm. The larvae of another fly, this of the Screwfly. This fly lays its eggs on open wounds. The maggots then emerge and burrow into the wound to feast on the host's flesh. These do not kill the host as they do not remain in the host for long before dropping off/chewing out to pupate in the ground. 

More on the screw worm 

Video of a Nasal Myiasis (I am not very squeamish and this was quite possibly one of the ickiest things I have ever seen.)

Gnathostomiasis or larva migrans profundus is introduced by eating poorly cooked fish, frogs, crustaceans and other meats. After incubation these larvae begin to eat their way from the digestive tract to the skin. Due to humans not being the usual vector for these parasites they do not complete their life cycle, are hard to detect and can cause many complications. This larvae migrates around beneath the surface of the skin. An in depth discussion here.

Life cycle of larva migrans profundus

Guinea worm is contracted through contaminated drinking water. This is a roundworm that starts in the intestinal tract and the female migrates the body. This female usually leaves the body through the feet and can be as large as a 3 foot long spaghetti noodle. One method of extracting these worms is to roll them around a stick and gently pull them out.
On the NY Times (A short documentary about the eradication efforts.
The Carter Center which is trying to eradicate the Guinea worm
On the CDC

Chigoe flea is a type of flea which burrows into the skin. Once inside it develops causing a painful, reddened swelling. Eventually a black dot appears on the swelling which is the hind legs, breathing organs and reproductive organs poking from the skin. While the flea is not directly harmful, secondary infections and large scale infestations can be very dangerous for the host. These fleas infect most warm-blooded hosts.
Video of the parasite from National Geographic

Question #10: Does eating sugar make you more likely to get sick?

A question from email and a complicated one.. the answer is yes... and well no.

One thing we must consider is the health of the person consuming the sugar in question. Those with immune diseases, diabetes, leukemia and digestive disorders (among other conditions) are going to have different experiences on health in this case than the average, healthy individual. Age and body size can also affect the case related to this question, partially, due to the body mass to sugar intake ratio. Of course a 40lbs child will be more effected by the large quantities of sugar than a 150lbs adult.

So, for the sake of this discussion we are going to assume that the individuals consuming the sugar is a healthy, average sized adult with no health conditions that will increase or decrease the effects of the sugar on the body.

The background

The only study discussing sugar and the immune system revolves around the behavior of neutrophils. Neutrophils are one type of immune cell found in the body. They are often in the blood but can also be found at sites of infection or cancer. These cells are usually the first ones to respond to infection or cancer due to their phagocytic nature, i.e. they come in and devour  the foreign or cancerous cells. There are several types of neutrophils that respond to different stimuli. The study does not seem to list which type(s) of neutrophils they are observing. This is problematic for deducing the actual impact of the sugar on the specific parts of the immune system.

The 1973 study I read started with individuals who have fasted. This means that they have not consumed food in 12-24 hours. Their body would be processing stored sugars at this point after exhausting the blood sugar (sugar in the blood). The subjects are then dosed with 20 or more teaspoons of sugar (different sources are used in studies such as honey, fructose, glucose, etc.) are then administered. After a wait time blood is drawn and added to a culture of bacteria. The neutrophil or other white blood cell activity is observed.

What did I find?

Aside from the 1973 study, which by science standards would be considered way out of date, I didn't uncover any scientific papers in peer reviewed journals that discussed humans and sugar intake. I was very disappointed as I searched around many distributors such as PubMed, EBSCOHost and several others and found nothing. I even tried different sugars to see if there would be papers for glucose or fructose instead of just sugar. I had no luck. I did find lots and lots of blogs and unreferenced sources that harken back to the 1973 study or no study at all.

What does that mean? Well there is one, outdated source, that suggest there may be a link. I say outdated because in most fields, particularly medicine, articles over 10 years old are considered sketchy to use and those 20 years or more are considered obsolete. The study suggests that it is the large inflow of sugar into the blood stream after fasting that depresses the immune system. The neutrophils are still working just a little slower.

Does this mean I will get sick from drinking a can of soda? No, probably not. Everything in moderation is how I have always felt. Perhaps with the recent interest in the subject more studies will be done to clarify what the outcome truly is. Below are links to the study and some relevant sources. Sadly, I can't give a better answer to this question until there is more research to read.


Sources:
Information about White Blood Cells
Blog Post about Immune System Cells
1973 Study most often cited
Blog post summarizing the study.
USA Today discussion of the study
Mouse Study - Note that the mice here are give 50g/kg of sugars which is much, much higher sugar to body weight dose than was used in the human study.
Another article that examines the study and raises the fact that no studies have really been conducted since 1973.
Another mouse study but it isn't only high sugar given but also high fat and cholesterol.

Question #9: What caused the black plague to spread?

This wonderfully upbeat question came through email.

The disease that caused the black death or black plague in Europe first appeared in the early 1300s in Asia. Some people in Europe were aware of the disease at this time but it had not yet been seen in Europe.

Black Death or Bubonic plague is caused by the bacteria Yersinia pestis and gets its name from the black pustules that form during the disease. These pustules appeared at the lymph nodes of the armpit and groin area. However, bubonic plague is not the only disease caused by Y. pestis. Septicemic plague, which is a blood infection, and pneumonic plague which affects the lungs and respiratory system are also caused by this bacteria. All three types of plague were likely responsible for deaths during the European outbreak in the 1300s.

When we discuss how the Black Plague spread through Europe we need to define two things: How did the plague arrive in Europe? (i.e. who or what was the vector to bring plague from Asia to Europe) and What was the progression through the different types of plague as it spread from its starting point in Europe to the rest of the continent?


The very first recording of this disease in Europe occurred in Kaffa (now called Feodosiya) a city in the Ukraine on the Black Sea coast. This city came under attack by Tartar's from Asia, approx 1347. The besieged city was happy to see their attackers dying in droves. The happiness was short-lived when the Tarters started catapulting their dead over the city wall.  The Tarters thought the smell of the decaying bodies would break the siege. When the dying Tarters fled the people of Kaffa also fled to Sicily.  Thus the black plague came to Europe from Asia.

From Eyewitness History

It is believed that the plague began its spread human to human via the septicemic (direct contact) method but later moved to the other forms as the plague spread.  There were a number of ways the bacteria spread during the Black Death event including via the air through coughing, fleas who were carrying the disease from rats and then biting humans, physical contact with the dead and dying as well as other methods. At its peak, it is believed that the plague was traveling 2-3 miles per day across Europe from the original site.

No one at the time was really sure how the plague was spreading quarantines were common as were people fleeing to other areas (which helped it spread faster if those who had contact fled). In coming ships were kept in quarantine off shore for 30 or more days to try and ensure the disease wasn't being carried. The only thing that was known for sure at the time was that the Black Death was very contagious and people died within days of the symptoms.

Many causes and ways to avoid the plague were written about. Causes were everything from bad air to the Jewish population with avoidance ranging from herbs and incense to not bathing and more.

By 1352 most areas of Europe were no longer plagued by the Black Death. In the 5 years it ravaged Europe, the Black Death spread to every corner of Europe, devastated the population and nearly crashed the entire economy of Europe. Approximately 1/3 or 20 million people died in those 5 years.


Resources:
http://www.history.com/topics/black-death
http://history.howstuffworks.com/historical-events/black-death.htm
http://www.eyewitnesstohistory.com/plague.htm