Nutritional status and reproduction Flashcards
General reproductive characteristics of Females
- Born with immature ova (eggs)
- Starting at puberty – ova mature about every 28 days (ovulation)
- Ova mature within follicles in the ovaries
General reproductive characteristics of males
- Born with sperm-producing systems
- Start producing sperm at puberty in response to testosterone – ongoing, not cyclic
What are the endocrine organs involved in the reproductive system?
- hypothalamus
- pituitary
- ovaries and placenta (adrenal glands, adipocytes)
- testes (adrenal glands)
Hormones from hypothalamus
GnRH - gonadotropin-releasing hormone
Hormones from pituitary
- Follicle-Stimulating Hormone (FSH) - acts on overaries to produce estrogen, progesterone and some testosterone and stimulates ovaries to produce eggs
- Luteinizing Hormone (LH): triggers release of an egg from the ovaries
Hormones from ovaries and placenta
- estrogen
- progesterone
- testosterone
Hormones from testes
testosterone
What is the HPG?
hypothalamus-anterior pituitary gonadal axis
* The connection between the hypothalamus, pituitary gland, and gonads. It is an important control mechanism mainly involved in the development and regulation of the reproductive system (and immune system and ageing)
* estrogen, progsterone and testosterone has a negative feedback loop to turn off hormonal release
What are the two phases of the menstrual cycle?
- follicular phase
- luteal phase
How do hormones change throughout the menstrual cycle?
Describe the follicular phase
Days 1-14
Low estrogen and progesterone → release of
GnRH → release of FSH and LH
* Growth and maturation of follicles and ova
* Release of estrogen (and progesterone)
* Thickening of outer uterine wall (endometrium)
* Peak LH levels stimulate ovulation (~day 14)
Describe the luteal phase
Days 15-28
Follicle becomes corpus luteum → releases
progesterone and some estrogen → further
endometrium development → inhibit GnRH
* If no fertilization: corpus luteum shrinks → progesterone and estrogen levels decline
* If fertilization: corpus luteum size increases → continued release of progesterone and estrogen
role of estrogen in the menstrual cycle
plays a role in ovulation (when your ovaries release an egg) and thickens the lining of your uterus (endometrium) to prepare it for pregnancy
Role of progesterone in the menstrual cycle
Progesterone creates a healthy uterine lining to support a fertilized egg, embryo and fetus
Role of FSH in the menstrual cycle
FSH helps control the menstrual cycle and stimulates the growth of eggs in the ovaries. FSH levels in women change throughout the menstrual cycle, with the highest levels happening just before an egg is released by the ovary. This is known as ovulation.
Role of LH in the menstrual cycle
LH helps control the menstrual cycle. It also triggers the release of an egg from the ovary. This is known as ovulation. LH levels quickly rise just before ovulation
Hormone effect on males
GnRH levels fluctuate → LH and FSH released → testosterone released from testes
Role of testosterone in male reproductive system
Testosterone and other androgens stimulate the maturation of sperm (70-80 days to mature)
* Mature sperm stored in epididymis until released (released in semen which contains fluid and nutrients)
Result of undernutrition in female fertility
hypothalamic amenorrhea
* disrupts the GnRH release, thus reducing others because the body senses that the organ is not capable of hosting an embyro
Result of undernutrition in male fertility
- Impaired sperm number, viability and motility
- Decreased sexual drive
What are the most common causes of undernutrition?
- negative energy balance
- weight loss
- low body fat (intense physical activity)
Role of antioxidants in fertility
protection of ovum/corpus luteum and sperm from reactive oxygen molecules
* ↓ intake associated with infertility
What micronutrients are important anitoxidants for fertility?
- vitamin C
- vitamin E
- beta-carotene
- selenium
Role of zinc in male fertility
role in testosterone synthesis and sperm maturation
Effect of obesity on fertility
Excess adipose tissue, particularly excess visceral adipose tissue, alters hormones involved in reproduction leading to infertility or subfertility in both females and males
What are the BMI classifications?
What is the health risk associated with each BMI?
Health risk associated with waist circumference
What occurs with the female menstrual cycle with obesity?
menstrual irregularities
* increased androgens (testosterone)
* increased leptin and estrogen
What disease occurs with increased androgens?
PCOS - polycystic ovary syndrome
* Hyperandrogenism (elevated testosterone)
* Impaired ovarian folliculagenesis (due to hyperinsulinemia)
* Associated with android fat distribution
Early etiology for developing PCOS
What occurs with male fertility with obesity?
Decreased sperm count and motility, increased risk of erectile dysfunction
* decreased testosterone
* leptin, estrogen
* increased scrotal temperature
What is the association betwen BMI and increased risk?
J shaped curved
What are some other nutritional factors that may be associated with female infertility?
- vegetarian/ vegan
- iron status
- alcohol
What are some other nutritional factors that may be associated with male infertility?
- vitamin D
- alcohol
- heavy metals, chemicals
What are the critical periods of fetal organ and tissue development?
- hyperplasia: increased cell multiplication (optimal nutrients critical)
- hyperplasia and hypertrophy
- hypertrophy: increased cell size
What are the 2 periods of growth?
- main embryonic period: 8 weeks
- fetal period: 9-38 weeks
What is the longest highly sensitive period?
CNS development up to ~16 weeks that is critical
* neural tube defects (NTDs)
* mental retardation
Why is nutritional status prior to pregnancy important?
Some critical periods of fetal development occur before women know they are pregnant
* If nutrients unavailable during critical period, can not ‘catch-up’ later (effects not reversible)
* Teratogens need period of time to clear
What are NTDs?
neural tube defects (NTDs)
* Failure of closure of the neural tube during early development; weeks 3-4
* various presentations and degree of severity
Formation of neural tube
Neural plate formed very early and has a series of folds that form the CNS and spinal chord.
* Result in formation of neural crest and spinal chord.
Prevalance of NTDs
NTDs most common congenital anomaly in US & Canada ~1.0-1.6 per 1000 live births
What are the types of NTDs?
- Anencephaly
- Encephalay
- Spina bifida
Anencephaly
incomplete brain formation, absence of forebrain and skull
Encephaly
protrusion of brain and membranes through skull (severity depends on length of exposure or area exposed)
Spina Bifida
incomplete spinal cord formation and “Lump” formation may have nervous tissue and will never be normal
* Control of muscles distal to (below) defect affected – often lower limbs, bladder
* If defect is high in spinal cord, death may occur
What micronutrient is essential in preventing NTDs?
Folate
Evidence of the link between folate and NTDs?
women who give birth to babies with NTDs usually have lower serum folate and dietary intake of folate
* epidemiological studies have shown regions with higher dietary folate intake have lower rates of NTDs
* women who take supplement containing folate before and during pregnancy have lower risk of having baby with NTDs
What vitamin is folate?
Vitamin B9
* water soluble
What are the folate family of compounds?
- Folate: polyglutamate found naturally in foods
- Folic Acid: monoglutamate more stable found in supplements and fortifed foods
- Bioactive Form: tetrahydrofolate
Main biological roles of folate
- DNA and RNA synthesis
- Methylation reactions
Describe the methylation cycle
- serum folate comes into cell with carrier to become 5-methyl tetrahydrofolate (via MTHFR)
- the methyl of 5-MeTHF is transferred to homocystein via VitB12to produce methionine
- Methionine reacts with ATP forming S-adenosylmethionine which is the principle donor for methylation
- Loss of methyl group from SAM forms AdoHcy which is converted to homocysteine for cycle to continue
What methylation processes is SAM involved with?
- DNA – gene regulation
- Protein – structure and function
- Lipid – synthesis
What is MTHFR?
Methylene tetrahydrofolate reductase
* rate-limiting enzyme in the methyl cycle that converts folate to 5-MeTHF and is coded by the MTHFR gene.
* regulates pathway
What is the connection between folate and NTDs?
Variety of factors
How does MTHFR gene effect NTDs?
Variant gene is associated with increased plasma homocysteine and risk of NTD
* CC – ‘normal’ MTHFR
* CT – heterozygous variant (est 40% population) and is increased risk of NTDs (OR 1.1 to 1.3)
* TT – homozygous variant (est 10% population) is higher increased risk of NTDs (OR 1.6 to 1.9)
How can reduced MTHFR be overcome?
dietary folate can bypass it to ensure methylation continues
How the MTHFR varient changes flux of methylation vs. nucleotide synthesis
Increased risk of NTDs if?
- dietary folate prior to and during pregnancy is inadequate
- genetic mutation of folate metabolism
What are the folate equivalents?
1Dietary Folate Equivalents (DFE)
* = 1 μg food folate
* = 0.6 μg synthetic folic acid with food
* = 0.5 μg synthetic folic acid from supplement on empty stomach
folic acid is more bioavailable
What are the folate requirements?
- RDA (adult females): 400μg/day
- RDA (pregnancy): 600μg/day
- UL (synthetic folic acid only): 1000μg/d
Folate supplementation reccomendations
Health Canada recommends women who can become pregnancy should take 400 μg synthetic folic acid/day from multivitamin supplement
* women do not generally meet recommendations
Food sources of naturally ocurring folate?
- Vegetables: peas (10 cups), beans, asparagus, dark leafy greens (only bioavailable when cooked)
- Fruits: oranges, orange juice, pineapple juice (juices highly bioavailable)
Food sources of fortified foods
Bread and grain products
* 150 μg folic acid /100g flour
* 200 ug folic acid/100g pasta
What are teratogens?
Substances that can produce or increase the incidence of an abnormality in embryonic or fetal development
* drugs (including alcohol), chemicals, infections, radiation
* vitamin A, lead, mercury
What is common cause for vitamin A toxicity?
Toxic level not usually from food but a result of:
* Mega dose supplements (Acne treatment)
* Retinoid drugs
Problem with retinoid drugs?
Such as isotretinoin (e.g. Accutane)
* increased risk of spontaneous abortion and birth defects
* craniofacial defects, cleft palate, cardiovascular and CNS abnormalities
* neuropsychological impairment later in life
Vitamin A DRIs for adult female?
- RDA: 700 ug/d
- UL: 3,000ug/d (pre-formed only)
What is the reccomendation for stopping retinoid drugs?
Stop use at least 6 months before pregnancy
* Stays stored in fat so have to wait a bit
Methyl mercury as a teratogen
Main food source of methyl mercury is
contaminated fish, diet high in mercury before and during pregnancy:
* CNS defects including cerebral atrophy, seizures, mental impairment, blindness
What fish are recommended to avoid?
fresh or frozen tuna, shark, marlin, orange roughy, escolar and canned albacore tuna
* Health Canada reports that most fish in
Canada have very low mercury levels.
Fish reccomendation for pregnant women
Women who are planning to get pregnant or those are currently pregnant are advised to have at least 150 g of cooked, low mercury fish each week (~2-3 servings)
* A good source of long chain omega-3 fatty acids that are important for fetal brain development
Alcohol as a teratogen
crosses the placenta and fetal liver can not metabolize because does not have the enzymes
* Most affected is CNS development which is a critical period through-out pregnancy
* Heavy alcohol intake increased risk of miscarriage, stillbirth and infant mortality
What is FASD?
fetal alcohol spectrum disorder (mild to severe)
* FAS
* FAE
What is FAS?
fetal alcohol syndrome
* growth impairment, neurological abnormalities, facial characteristics
* developmental delays, behavioral and learning disabilities which some effects may not show up until the child is older
What is the most common cause of impaired mental functioning?
Alcohol consumption during pregnancy
